U.S. patent application number 12/311560 was filed with the patent office on 2010-01-21 for processing end point detection method, polishing method,and polishing apparatus.
Invention is credited to Yoichi Kobayashi, Koji Maruyama, Ryuichiro Mitani, Shunsuke Nakai, Shinro Ohta, Atsushi Shigeta, Noburu Shimizu.
Application Number | 20100015889 12/311560 |
Document ID | / |
Family ID | 39282970 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100015889 |
Kind Code |
A1 |
Shimizu; Noburu ; et
al. |
January 21, 2010 |
Processing end point detection method, polishing method,and
polishing apparatus
Abstract
The present invention relates to a processing end point
detection method for detecting a timing of a processing end point
(e.g., polishing stop, changing of polishing conditions) by
calculating a characteristic value of a surface of a workpiece (an
object of polishing) such as a substrate. This method includes
producing a spectral waveform indicating a relationship between
reflection intensities and wavelengths at a processing end point,
with use of a reference workpiece or simulation calculation, based
on the spectral waveform, selecting wavelengths of a local maximum
value and a local minimum value of the reflection intensities,
calculating the characteristic value with respect to a surface, to
be processed, from reflection intensities at the selected
wavelengths, setting a distinctive point of time variation of the
characteristic value at a processing end point of the workpiece as
the processing end point, and detecting the processing end point of
the workpiece by detecting the distinctive point during processing
of the workpiece.
Inventors: |
Shimizu; Noburu; (Tokyo,
JP) ; Ohta; Shinro; (Tokyo, JP) ; Maruyama;
Koji; (Tokyo, JP) ; Kobayashi; Yoichi; (Tokyo,
JP) ; Mitani; Ryuichiro; (Tokyo, JP) ; Nakai;
Shunsuke; (Tokyo, JP) ; Shigeta; Atsushi;
(Kanagawa, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
39282970 |
Appl. No.: |
12/311560 |
Filed: |
October 5, 2007 |
PCT Filed: |
October 5, 2007 |
PCT NO: |
PCT/JP2007/070030 |
371 Date: |
April 3, 2009 |
Current U.S.
Class: |
451/5 ; 451/287;
451/41; 451/6 |
Current CPC
Class: |
G01N 21/55 20130101;
B24B 49/04 20130101; B24B 37/013 20130101; G05B 19/406 20130101;
G01B 11/0675 20130101; H01L 22/26 20130101; B24D 7/12 20130101;
G05B 19/4065 20130101; B24B 49/16 20130101; G01N 21/9501 20130101;
B24B 49/12 20130101; H01L 2924/0002 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
451/5 ; 451/6;
451/41; 451/287 |
International
Class: |
B24B 49/04 20060101
B24B049/04; B24B 49/12 20060101 B24B049/12; B24B 37/04 20060101
B24B037/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 2006 |
JP |
JP2006-274622 |
Dec 7, 2006 |
JP |
JP2006-330383 |
Claims
1. A processing end point detection method for detecting a
processing end point based on a characteristic value with respect
to a surface of a workpiece, the characteristic value being
calculated using a spectral waveform of reflected light obtained by
applying light to the surface of the workpiece, said method
comprising: producing a spectral waveform indicating a relationship
between reflection intensities and wavelengths at a processing end
point, with use of a reference workpiece or simulation calculation;
based on the spectral waveform, selecting wavelengths of a local
maximum value and a local minimum value of the reflection
intensities; calculating the characteristic value with respect to a
surface, to be processed, from reflection intensities at the
selected wavelengths; setting a distinctive point of time variation
of the characteristic value at a processing end point of a
workpiece as the processing end point; and detecting the processing
end point of the workpiece by detecting the distinctive point
during processing of the workpiece.
2. The processing end point detection method according to claim 1,
further comprising: averaging the reflection intensities at each
wavelength over a processing time of the reference workpiece to
determine an average reflection intensity at each wavelength; and
producing a reference spectral waveform by dividing each of the
reflection intensities, obtained at the processing end point of the
reference workpiece, by the corresponding average reflection
intensity, wherein said selecting of the wavelengths of the local
maximum value and the local minimum value is performed based on the
reference spectral waveform.
3. The processing end point detection method according to claim 1,
further comprising: defining a weight function having a weight
centered on the selected wavelength of the local maximum value,
wherein said calculating of the characteristic value comprises
determining the characteristic value with respect to the surface of
the workpiece by multiplying the reflection intensities, obtained
by application of the light to the surface of the workpiece, by the
weight function and integrating the resultant reflection
intensities, and said detecting of the processing end point
comprises detecting the processing end point of the workpiece by
detecting a distinctive point of time variation of the
characteristic value.
4. The processing end point detection method according to claim 1,
further comprising shifting the selected wavelengths to shorter or
longer wavelengths.
5. A processing end point detection method of detecting a
processing end point based on a characteristic value with respect
to a surface of a workpiece, the characteristic value being
calculated using a spectral waveform of reflected light obtained by
applying multiwavelength light to the surface of the workpiece,
said method comprising: averaging reflection intensities at each
wavelength over a processing time to determine an average
reflection intensity at each wavelength, with use of a reference
workpiece or simulation calculation; producing a reference spectral
waveform by dividing each of reflection intensities, obtained by
application of the multi wavelength light to the surface of the
workpiece during processing thereof, by the corresponding average
reflection intensity; and detecting a processing end point of the
workpiece by monitoring the reference spectral waveform.
6. A processing apparatus comprising: a light source configured to
apply light to a surface of a workpiece; a light-receiving unit
configured to receive reflected light from the surface of the
workpiece; a spectroscope unit configured to divide the reflected
light received by said light-receiving unit into a plurality of
light rays and convert the light rays into electrical information;
and a processor configured to process the electrical information
from said spectroscope unit, wherein said processor is configured
to average reflection intensities at each wavelength over a
processing time of a reference workpiece to determine an average
reflection intensity at each wavelength, produce a reference
spectral waveform by dividing each of the reflection intensities,
obtained at the processing end point of the reference workpiece, by
the corresponding average reflection intensity, select wavelengths
of a local maximum value and a local minimum value of the reference
spectral waveform, calculating the characteristic value with
respect to a surface of the reference workpiece from reflection
intensities at the selected wavelengths, set a distinctive point of
time variation of the characteristic value at a processing end
point of a workpiece as a processing end point, and detect the
processing end point of the workpiece by detecting the distinctive
point during processing of the workpiece.
7. The processing apparatus according to claim 6, wherein said
processor is configured to shift the selected wavelengths TO
shorter or longer wavelengths.
8. The processing apparatus according to claim 6, wherein said
processor is configured to define a weight function having a weight
centered on the selected wavelength of the local maximum value,
determine the characteristic value with respect to the surface of
the workpiece by multiplying the reflection intensities, obtained
by application of the light to the surface of the workpiece, by the
weight function and integrating the resultant reflection
intensities, and detect the processing end point of the workpiece
by detecting a distinctive point of time variation of the
characteristic value.
9. A processing apparatus comprising: a light source configured to
apply multiwavelength light to a surface of a workpiece; a
light-receiving unit configured to receive reflected light from the
surface of the workpiece; a spectroscope unit configured to divide
the reflected light received by said light-receiving unit into a
plurality of light rays and convert the light rays into electrical
information; and a processor configured to process the electrical
information from said spectroscope unit, wherein said processor is
configured to average reflection intensities at each wavelength
over a processing time of a reference workpiece to determine an
average reflection intensity at each wavelength, produce a
reference spectral waveform by dividing each of reflection
intensities, obtained by application of the multiwavelength light
to the surface of the workpiece during processing thereof, by the
corresponding average reflection intensity, and detect a processing
end point of the workpiece by monitoring the reference spectral
waveform.
10. A polishing method, comprising: holding and rotating a
workpiece by a top ring; pressing the workpiece against a polishing
surface on a rotating polishing table to polish the workpiece; and
monitoring a surface state of the workpiece with a sensor provided
on the polishing table during polishing of the workpiece, wherein a
rotational speed of the top ring and a rotational speed of the
polishing table are set such that paths of the sensor, described on
a surface of the workpiece in a predetermined measuring time, are
distributed substantially evenly over an entire circumference of
the surface of the workpiece.
11. The polishing method according to claim 10, wherein the
rotational speed of the top ring and the rotational speed of the
polishing table are set such that a path of the sensor rotates
about 0.5.times.N times on the surface of the workpiece in the
predetermined measuring time, where N is a natural number.
12. The polishing method according to claim 10, wherein the
predetermined measuring time is a moving average time which is used
in moving average performed on monitoring signals obtained by the
sensor.
13. The polishing method according to claim 10, further comprising:
detecting a polishing end point by said monitoring of the surface
state of the workpiece by the sensor.
14. The polishing method according to claim 10, wherein during said
monitoring of the surface state of the workpiece by the sensor,
polishing of the workpiece is performed so as to provide a uniform
film thickness of the surface of the workpiece.
15. The polishing method according to claim 10, wherein the
predetermined measuring time is a time required for the polishing
table to make a predetermined number of revolutions which is
selected from among natural numbers from 4 to 16.times.V, where V
represents the rotational speed of the polishing table.
16. A polishing method, comprising: holding and rotating a
workpiece by a top ring; pressing the workpiece against a polishing
surface on a rotating polishing table to polish the workpiece; and
monitoring a surface state of the workpiece with a sensor provided
on the polishing table during polishing of the workpiece, wherein a
rotational speed of the top ring and a rotational speed of the
polishing table are set such that, while the polishing table makes
a predetermined number of revolutions which is expressed by a first
natural number, the top ring makes a predetermined number of
revolutions which is expressed by a second natural number, the
first natural number and the second natural number are relatively
prime, and the first natural number is not less that 4 and not more
than a number of revolutions the polishing table makes within 16
seconds.
17. The polishing method according to claim 16, further comprising:
detecting a polishing end point by said monitoring of the surface
state of the workpiece by the sensor.
18. The polishing method according to claim 16, further comprising:
during said monitoring of the surface state of the workpiece by the
sensor, polishing the workpiece so as to provide a uniform film
thickness of the surface of the workpiece.
19. A polishing method comprising: holding and rotating a workpiece
by a top ring; pressing the workpiece against a polishing surface
on a rotating polishing table to polish the workpiece; and
monitoring a surface state of the workpiece with a sensor provided
on the polishing table during polishing of the workpiece, wherein a
rotational speed of the top ring and a rotational speed of the
polishing table satisfy a relational expression given by
nV/m-1.ltoreq.R.ltoreq.nV/m+1 or mR/n-1.ltoreq.V.ltoreq.mR/n+1
where V is the rotational speed of the polishing table and is a
natural number indicating a multiple of a setting unit that is
allowed by a polishing apparatus, R is the rotational speed of the
top ring and is a natural number indicating a multiple of the
setting unit that is allowed by the polishing apparatus, m is a
predetermined natural number that indicates the number of
revolutions the polishing table makes while the sensor travels
across the surface of the workpiece in directions or orientations
distributed evenly in a circumferential direction of the workpiece
over an entire circumference thereof, and n is a natural number
such that m and n are relatively prime.
20. The polishing method according to claim 19, further comprising:
detecting a polishing end point by said monitoring of the surface
state of the workpiece by the sensor.
21. The polishing method according to claim 19, wherein during said
monitoring of the surface state of the workpiece by the sensor,
polishing of the workpiece is performed so as to provide a uniform
film thickness of the surface of the workpiece.
22. A polishing apparatus comprising: a top ring configured to hold
and rotate a workpiece; a rotatable polishing table having a
polishing surface, said top ring being configured to press the
workpiece against the polishing surface; and a sensor provided on
said polishing table and configured to monitor a surface state of
the workpiece during polishing of the workpiece, wherein a
rotational speed of said top ring and a rotational speed of said
polishing table are set such that paths of the sensor, described on
a surface of the workpiece in a predetermined measuring time, are
distributed substantially evenly over an entire circumference of
the surface of the workpiece.
23. The polishing apparatus according to claim 22, wherein the
rotational speed of said top ring and the rotational speed of said
polishing table are set such that a path of the sensor rotates
about 0.5.times.N times on the surface of the workpiece in the
predetermined measuring time, where N is a natural number.
24. The polishing apparatus according to claim 22, wherein the
predetermined measuring time is a moving average time which is used
in moving average performed on monitoring signals obtained by the
sensor.
25. The polishing apparatus according to claim 22, further
comprising: an end point detector configured to detect a polishing
end point based on the surface state of the workpiece obtained by
said sensor.
26. The polishing apparatus according to claim 22, further
comprising: a controller configured to determine forces of pressing
the workpiece against the polishing surface so as to uniformly
polish the surface of the workpiece, based on the surface state of
the workpiece by said sensor.
27. The polishing apparatus according to claim 22, wherein the
predetermined measuring time is a time required for said polishing
table to make a predetermined number of revolutions which is
selected from among natural numbers from 4 to 16.times.V, where V
represents the rotational speed of said polishing table.
28. A polishing apparatus comprising: a top ring configured to hold
and rotate a workpiece; a rotatable polishing table having a
polishing surface, said top ring being configured to press the
workpiece against the polishing surface; and a sensor provided on
said polishing table and configured to monitor a surface state of
the workpiece during polishing of the workpiece, wherein a
rotational speed of said top ring and a rotational speed of said
polishing table are set such that, while said polishing table makes
a predetermined number of revolutions which is expressed by a first
natural number, said top ring makes a predetermined number of
revolutions which is expressed by a second natural number, the
first natural number and the second natural number are relatively
prime, and the first natural number is not less that 4 and not more
than a number of revolutions said polishing table makes within 16
seconds.
29. The polishing apparatus according to claim 28, further
comprising: an end point detector configured to detect a polishing
end point based on the surface state of the workpiece obtained by
said sensor.
30. The polishing apparatus according to claim 28, further
comprising: a controller configured to determine forces of pressing
the workpiece against the polishing surface so as to uniformly
polish the surface of the workpiece, based on the surface state of
the workpiece by said sensor.
31. A polishing apparatus comprising: a top ring configured to hold
and rotate a workpiece; a rotatable polishing table having a
polishing surface, said top ring being configured to press the
workpiece against the polishing surface; and a sensor provided on
said polishing table and configured to monitor a surface state of
the workpiece during polishing of the workpiece, wherein a
rotational speed of said top ring and a rotational speed of said
polishing table satisfy a relational expression given by
nV/m-1.ltoreq.R.ltoreq.nV/m+1 or mR/n-1.ltoreq.V.ltoreq.mR/n+1
where V is the rotational speed of said polishing table and is a
natural number indicating a multiple of a setting unit that is
allowed by a polishing apparatus, R is the rotational speed of said
top ring and is a natural number indicating a multiple of the
setting unit that is allowed by the polishing apparatus, m is a
predetermined natural number that indicates the number of
revolutions said polishing table makes while the sensor travels
across the surface of the workpiece in directions or orientations
distributed evenly in a circumferential direction of the workpiece
over an entire circumference thereof, and n is a natural number
such that m and n are relatively prime.
32. The polishing apparatus according to claim 31, further
comprising: an end point detector configured to detect a polishing
end point based on the surface state of the workpiece obtained by
said sensor.
33. The polishing apparatus according to claim 31, further
comprising: a controller configured to determine forces of pressing
the workpiece against the polishing surface so as to uniformly
polish the surface of the workpiece, based on the surface state of
the workpiece by said sensor.
34. A polishing apparatus comprising: a top ring configured to hold
and rotate a workpiece; a rotatable polishing table having a
polishing surface, said top ring being configured to press the
workpiece against the polishing surface; a sensor provided on said
polishing table and configured to monitor a surface state of the
workpiece during polishing of the workpiece; and a monitoring
device configured to process signal from said sensor, wherein a
rotational speed of said top ring and a rotational speed of said
polishing table are set such that said sensor travels across a
surface of the workpiece in a different path every time said sensor
scans the surface of the workpiece, and said monitoring device is
configured to calculate an average of signal values obtained along
plural paths of said sensor which rotate around the surface of the
workpiece and provide a set of sensor paths.
35. The polishing apparatus according to claim 34, further
comprising: an end point detector configured to detect a polishing
end point based on the surface state of the workpiece obtained by
said sensor.
36. The polishing apparatus according to claim 34, further
comprising: a controller configured to determine forces of pressing
the workpiece against the polishing surface so as to uniformly
polish the surface of the workpiece, based on the surface state of
the workpiece by said sensor.
Description
TECHNICAL FIELD
[0001] The present invention relates to a processing end point
detection method for detecting a timing of a processing end point
(e.g., polishing stop, changing of polishing conditions, etching
stop, film-formation stop, and the like) by calculating a
characteristic value of a surface of a workpiece (an object of
polishing) such as a substrate.
[0002] The present invention also relates to a polishing method and
polishing apparatus for polishing a substrate, such as a
semiconductor wafer, to planarize the substrate.
BACKGROUND ART
[0003] The trend of recent years in a semiconductor device has been
a highly integrated structure, which requires fine interconnects
and multi-layered structure. To realize the fine interconnects and
the multi-layered structure, it is necessary to planarize a surface
of a substrate. Chemical mechanical polishing (CMP) is
conventionally used to remove irregularities from the surface of
the substrate to thereby planarize the surface.
[0004] In the chemical mechanical polishing process, polishing
operation has to be stopped at a desired point after the substrate
has been polished for a predetermined period of time. For example,
it may be desirable to leave an insulating layer, such as
SiO.sub.2, (such an insulating layer is referred to as an
interlevel film because a layer, e.g., a metal layer, is further
formed on the insulating layer in a subsequent process) on metal
interconnects of Cu or Al. In this case, if the substrate is
polished more than required, a surface of a lower-level metal film
is exposed. Therefore, the polishing process needs to be finished
so as to leave the interlevel film with a predetermined
thickness.
[0005] In the fabrication process of the semiconductor device, a
predetermined pattern of interconnect trenches is formed on a
surface of a substrate, and the interconnect trenches are filled up
with Cu (copper) or its alloy. Then, unwanted portions of Cu or its
alloy are removed from the surface of the substrate by the chemical
mechanical polishing (CMP). When the Cu layer is polished by the
CMP process, it is necessary to selectively remove the Cu layer
from the substrate so as to leave only the Cu layer in the
interconnect trenches. Specifically, it is necessary to remove the
Cu layer in areas other than the interconnect trenches until the
insulating film (which is made from SiO.sub.2 or the like) is
exposed.
[0006] In this case, if the Cu layer in the interconnect trenches
is excessively polished off together with the insulating film, a
circuit resistance can increase and the entire substrate has to be
discarded, resulting in a large loss. On the other hand, if the Cu
layer is polished insufficiently and remains on the insulating
film, circuits are not separated well and short-circuit occurs. As
a result, polishing of the Cu layer should be performed again,
resulting in an increased manufacturing cost.
[0007] There has been known a polishing state monitoring apparatus
for measuring an intensity of a reflected light using an optical
sensor and detecting an end point of the CMP process based on the
measured intensity of the reflected light. This polishing state
monitoring apparatus includes the optical sensor having a
light-emitting element and a light-detecting element. Light is
applied from the optical sensor to a surface of a substrate during
polishing of the surface. An end point of the CMP process is
determined from a change in reflection intensity of the light from
the surface of the substrate.
[0008] The following methods are known for measuring optical
characteristics in the above-mentioned CMP process.
[0009] (1) Light from a monochromatic light source, such as a
semiconductor laser or a light-emitting diode (LED), is applied to
the surface, being polished, of the substrate and a change in the
intensity of reflected light is detected.
[0010] (2) White light is applied to the surface of the substrate,
and a spectral (ratio) reflection intensity is compared with a
pre-stored spectral (ratio) reflection intensity for a polishing
end point.
[0011] There has recently been developed a polishing state
monitoring apparatus constructed to estimate an initial film
thickness of a substrate, apply a laser beam to the substrate, and
approximate a time variation of measurements of the intensity of
reflected light from the substrate with a sine-wave model function
to thereby calculate a film thickness.
[0012] There has also been proposed a method of detecting a
polishing end point based on a time variation of a characteristic
value of a substrate. This characteristic value is calculated by
multiplying spectral data, obtained by applying light to the
substrate, by a weight function and integrating the resultant
spectral data (for example, see Japanese laid-open patent
publication No. 2004-154928).
[0013] However, in the above-described conventional methods, it is
difficult to detect a distinctive point (i.e., a point of
distinctive change in the reflection intensity or the
characteristic value) which serves as an index indicating a
polishing end point. This makes it difficult to detect an accurate
polishing end point. For example, when using a monochromatic light
source, a relationship between a film thickness and a signal of the
reflection intensity is determined uniquely according to a
wavelength of the light source. In this case, the distinctive point
may not always appear when a target film thickness, i.e., a
polishing end point, is reached. Moreover, it is difficult to
correct the manner of appearance.
[0014] On the other hand, when using a multiwavelength light such
as white light, it is possible to select a desired wavelength so
that a distinctive point of the reflection intensity appears when a
desired film thickness is reached. However, selection of an optimum
wavelength for a structure of a workpiece entails trial and error.
As a result, a lot of time is needed for the selection process.
Moreover, it is difficult to verify whether the wavelength selected
is best suited.
[0015] A polishing apparatus having a top ring with multiple
chambers therein is known as an apparatus for performing the
above-mentioned CMP. This type of polishing apparatus is capable of
adjusting pressures in the chambers independently. In this
polishing apparatus, a sensor is provided so as to measure a
physical quantity associated with a thickness of a film on a
substrate and a monitoring signal is produced based on this
physical quantity. Prior to polishing of the substrate, a reference
signal that indicates a relationship between the monitoring signal
and times is prepared in advance. During polishing of the
substrate, pressing forces of the top ring are adjusted such that
monitoring signals, obtained at plural measuring points on the
substrate, converge on the reference signal, whereby a uniform film
thickness can be realized over the surface of the substrate (for
example, see WO 2005/123335).
[0016] A highly-functional CPU has recently been developed with the
trend of a high-speed and highly-integrated semiconductor device.
This highly-functional CPU incorporates therein several functions
including a memory section and a calculating section in a single
semiconductor chip. In this semiconductor chip, areas with
different pattern densities and different structures coexist.
Moreover, a chip size has becoming larger year by year, and some
types of CCD devices have a film size of 24.times.36 mm. In
semiconductor fabrications, a lot of chips are formed on a single
substrate. Therefore, areas with different pattern densities and
different structures coexist in a surface of the substrate.
Further, for the purpose of evaluating a finished device, a
substrate may have an electrical characteristic evaluation pattern
that is greatly different from device patterns.
[0017] When polishing such a substrate, a change in thickness of a
film on a surface of the substrate is monitored by applying light
to the surface of the substrate and detecting the reflected light
from the substrate by an optical sensor. However, the intensity of
the reflected light from the surface of the substrate varies
intricately depending not only on the change in film thickness as a
result of polishing, but also on the patterns and structures of the
devices. Specifically, since a polishing table and a top ring are
rotating during polishing, the optical sensor, which is provided in
the polishing table, passes through different areas with different
pattern densities and different structures every time the sensor
scans the surface of the substrate. Consequently, the intensity of
the reflected light can vary due to the influence of the device
patterns and structures. This varying reflection intensity is
superimposed as a noise on a signal indicating a change in the film
thickness. In such a case, even if smoothing of the signal is
performed, the change in film thickness cannot be accurately
monitored because the noise is large. This affects an accuracy of
polishing end point detection and a polishing control for a uniform
film thickness.
[0018] In a case where an object of polishing is a copper film, an
eddy current sensor is often used to measure a film thickness.
Typically, the copper film is formed by plating. A plating
apparatus for performing copper plating generally has cathode
electrodes arranged at equal intervals along a periphery of a
substrate. A plating solution is supplied to a surface of the
substrate, with the plating solution being retained by a seal
member. In this state, a voltage is applied between the cathode
electrodes and an anode electrode in the plating solution to
thereby plate the surface of the substrate with copper. Use of such
a plating apparatus can present a problem of variations in film
thickness along the periphery of the substrate because of
variations in contact resistance of the cathode electrodes or
because of sealing performance of the seal member. As a result, the
sensor may scan only thick portions or thin portions of the film
depending on times during polishing, thus failing to measure an
average film thickness.
DISCLOSURE OF INVENTION
[0019] The present invention has been made in view of the above
drawbacks. It is therefore a first object of the present invention
to provide a processing end point detection method and a processing
apparatus capable of easily obtaining a characteristic value that
has a distinctive point, such as a local maximal value or a local
minimal value, at a target film thickness to realize an accurate
processing end point detection.
[0020] It is a second object of the present invention to provide a
polishing method and a polishing apparatus capable of reducing an
influence of various areas with different pattern densities and
different structures or variations in film thickness along a
circumferential direction produced in a film formation process on
an output signal of a sensor to realize an accurate polishing end
point detection and a uniform film thickness.
[0021] In order to achieve the first object, the present invention
provides a processing end point detection method for detecting a
processing end point based on a characteristic value with respect
to a surface of a workpiece, the characteristic value being
calculated using a spectral waveform of reflected light obtained by
applying light to the surface of the workpiece. The method
includes: producing a spectral waveform indicating a relationship
between reflection intensities and wavelengths at a processing end
point, with use of a reference workpiece or simulation calculation;
based on the spectral waveform, selecting wavelengths of a local
maximum value and a local minimum value of the reflection
intensities; calculating the characteristic value with respect to a
surface, to be processed, from reflection intensities at the
selected wavelengths; setting a distinctive point of time variation
of the characteristic value at a processing end point of a
workpiece as the processing end point; and detecting the processing
end point of the workpiece by detecting the distinctive point
during processing of the workpiece.
[0022] Examples of the processing of the workpiece include
polishing of a substrate having a film thereon and forming a film
on a substrate.
[0023] In a preferred aspect of the present invention, the method
further includes averaging the reflection intensities at each
wavelength over a processing time of the reference workpiece to
determine an average reflection intensity at each wavelength; and
producing a reference spectral waveform by dividing each of the
reflection intensities, obtained at the processing end point of the
reference workpiece, by the corresponding average reflection
intensity. The selecting of the wavelengths of the local maximum
value and the local minimum value is performed based on the
reference spectral waveform.
[0024] In a preferred aspect of the present invention, the method
further includes defining a weight function having a weight
centered on the selected wavelength of the local maximum value,
wherein the calculating of the characteristic value comprises
determining the characteristic value with respect to the surface of
the workpiece by multiplying the reflection intensities, obtained
by application of the light to the surface of the workpiece, by the
weight function and integrating the resultant reflection
intensities, and the detecting of the processing end point
comprises detecting the processing end point of the workpiece by
detecting a distinctive point of time variation of the
characteristic value.
[0025] In a preferred aspect of the present invention, the method
further includes shifting the selected wavelengths to shorter or
longer wavelengths.
[0026] Another aspect of the present invention provides a
processing end point detection method of detecting a processing end
point based on a characteristic value with respect to a surface of
a workpiece, the characteristic value being calculated using a
spectral waveform of reflected light obtained by applying
multiwavelength light to the surface of the workpiece. The method
includes averaging reflection intensities at each wavelength over a
processing time to determine an average reflection intensity at
each wavelength, with use of a reference workpiece or simulation
calculation; producing a reference spectral waveform by dividing
each of reflection intensities, obtained by application of the
multiwavelength light to the surface of the workpiece during
processing thereof, by the corresponding average reflection
intensity; and detecting a processing end point of the workpiece by
monitoring the reference spectral waveform.
[0027] Another aspect of the present invention provides a
processing apparatus including: a light source configured to apply
light to a surface of a workpiece; a light-receiving unit
configured to receive reflected light from the surface of the
workpiece; a spectroscope unit configured to divide the reflected
light received by the light-receiving unit into a plurality of
light rays and convert the light rays into electrical information;
and a processor configured to process the electrical information
from the spectroscope unit. The processor is configured to average
reflection intensities at each wavelength over a processing time of
a reference workpiece to determine an average reflection intensity
at each wavelength, produce a reference spectral waveform by
dividing each of the reflection intensities, obtained at the
processing end point of the reference workpiece, by the
corresponding average reflection intensity, select wavelengths of a
local maximum value and a local minimum value of the reference
spectral waveform, calculating the characteristic value with
respect to a surface of the reference workpiece from reflection
intensities at the selected wavelengths, set a distinctive point of
time variation of the characteristic value at a processing end
point of a workpiece as a processing end point, and detect the
processing end point of the workpiece by detecting the distinctive
point during processing of the workpiece.
[0028] Another aspect of the present invention provides a
processing apparatus including: a light source configured to apply
multiwavelength light to a surface of a workpiece; a
light-receiving unit configured to receive reflected light from the
surface of the workpiece; a spectroscope unit configured to divide
the reflected light received by the light-receiving unit into a
plurality of light rays and convert the light rays into electrical
information; and a processor configured to process the electrical
information from the spectroscope unit. The processor is configured
to average reflection intensities at each wavelength over a
processing time of a reference workpiece to determine an average
reflection intensity at each wavelength, produce a reference
spectral waveform by dividing each of reflection intensities,
obtained by application of the multiwavelength light to the surface
of the workpiece during processing thereof, by the corresponding
average reflection intensity, and detect a processing end point of
the workpiece by monitoring the reference spectral waveform.
[0029] According to the present invention as described above, it is
possible to obtain the characteristic value which has a distinctive
changing point at the polishing end point and has a good
signal-to-noise ratio depending on a device pattern of a substrate.
Therefore, an accurate polishing end point can be detected.
[0030] In order to achieve the second object, the present invention
provides a polishing method including: holding and rotating a
workpiece by a top ring; pressing the workpiece against a polishing
surface on a rotating polishing table to polish the workpiece, and
monitoring a surface state of the workpiece with a sensor provided
on the polishing table during polishing of the workpiece. A
rotational speed of the top ring and a rotational speed of the
polishing table are set such that paths of the sensor, described on
a surface of the workpiece in a predetermined measuring time, are
distributed substantially evenly over an entire circumference of
the surface of the workpiece.
[0031] In a preferred aspect of the present invention, the
rotational speed of the top ring and the rotational speed of the
polishing table are set such that a path of the sensor rotates
about 0.5.times.N times on the surface of the workpiece in the
predetermined measuring time, where N is a natural number.
[0032] In a preferred aspect of the present invention, the
predetermined measuring time is a moving average time which is used
in moving average performed on monitoring signals obtained by the
sensor.
[0033] In a preferred aspect of the present invention, the method
further includes detecting a polishing end point by the monitoring
of the surface state of the workpiece by the sensor.
[0034] In a preferred aspect of the present invention, during the
monitoring of the surface state of the workpiece by the sensor,
polishing of the workpiece is performed so as to provide a uniform
film thickness of the surface of the workpiece.
[0035] In a preferred aspect of the present invention, the
predetermined measuring time is a time required for the polishing
table to make a predetermined number of revolutions which is
selected from among natural numbers from 4 to 16.times.V, where V
represents the rotational speed of the polishing table.
[0036] Another aspect of the present invention provides a polishing
method including: holding and rotating a workpiece by a top ring;
pressing the workpiece against a polishing surface on a rotating
polishing table to polish the workpiece; and monitoring a surface
state of the workpiece with a sensor provided on the polishing
table during polishing of the workpiece. A rotational speed of the
top ring and a rotational speed of the polishing table are set such
that, while the polishing table makes a predetermined number of
revolutions which is expressed by a first natural number, the top
ring makes a predetermined number of revolutions which is expressed
by a second natural number, the first natural number and the second
natural number are relatively prime, and the first natural number
is not less that 4 and not more than a number of revolutions the
polishing table makes within 16 seconds.
[0037] Another aspect of the present invention provides a polishing
method including: holding and rotating a workpiece by a top ring;
pressing the workpiece against a polishing surface on a rotating
polishing table to polish the workpiece; and monitoring a surface
state of the workpiece with a sensor provided on the polishing
table during polishing of the workpiece. A rotational speed of the
top ring and a rotational speed of the polishing table satisfy a
relational expression given by
nV/m-1.ltoreq.R.ltoreq.nV/m+1 or mR/n-1.ltoreq.V.ltoreq.mR/n+1
[0038] where V is the rotational speed of the polishing table and
is a natural number indicating a multiple of a setting unit that is
allowed by a polishing apparatus, K is the rotational speed of the
top ring and is a natural number indicating a multiple of the
setting unit that is allowed by the polishing apparatus, m is a
predetermined natural number that indicates the number of
revolutions the polishing table makes while the sensor travels
across the surface of the workpiece in directions or orientations
distributed evenly in a circumferential direction of the workpiece
over an entire circumference thereof, and n is a natural number
such that m and n are relatively prime.
[0039] Another aspect of the present invention provides a polishing
apparatus including: a top ring configured to hold and rotate a
workpiece; a rotatable polishing table having a polishing surface,
the top ring being configured to press the workpiece against the
polishing surface; and a sensor provided on the polishing table and
configured to monitor a surface state of the workpiece during
polishing of the workpiece. A rotational speed of the top ring and
a rotational speed of the polishing table are set such that paths
of the sensor, described on a surface of the workpiece in a
predetermined measuring time, are distributed substantially evenly
over an entire circumference of the surface of the workpiece.
[0040] Another aspect of the present invention provides a polishing
apparatus including: a top ring configured to hold and rotate a
workpiece; a rotatable polishing table having a polishing surface,
the top ring being configured to press the workpiece against the
polishing surface; and a sensor provided on the polishing table and
configured to monitor a surface state of the workpiece during
polishing of the workpiece. A rotational speed of the top ring and
a rotational speed of the polishing table are set such that, while
the polishing table makes a predetermined number of revolutions
which is expressed by a first natural number, the top ring makes a
predetermined number of revolutions which is expressed by a second
natural number, the first natural number and the second natural
number are relatively prime, and the first natural number is not
less that 4 and not more than a number of revolutions the polishing
table makes within 16 seconds.
[0041] Another aspect of the present invention provides a polishing
apparatus including: a top ring configured to hold and rotate a
workpiece; a rotatable polishing table having a polishing surface,
the top ring being configured to press the workpiece against the
polishing surface; and a sensor provided on the polishing table and
configured to monitor a surface state of the workpiece during
polishing of the workpiece. A rotational speed of the top ring and
a rotational speed of the polishing table satisfy a relational
expression given by
nV/m-1.ltoreq.R.ltoreq.nV/m+1 or mR/n-1.ltoreq.V.ltoreq.mR/n+1
[0042] where V is the rotational speed of the polishing table and
is a natural number indicating a multiple of a setting unit that is
allowed by a polishing apparatus, R is the rotational speed of the
top ring and is a natural number indicating a multiple of the
setting unit that is allowed by the polishing apparatus, m is a
predetermined natural number that indicates the number of
revolutions the polishing table makes while the sensor travels
across the surface of the workpiece in directions or orientations
distributed evenly in a circumferential direction of the workpiece
over an entire circumference thereof, and n is a natural number
such that m and n are relatively prime.
[0043] Another aspect of the present invention provides a polishing
apparatus including: a top ring configured to hold and rotate a
workpiece, a rotatable polishing table having a polishing surface,
the top ring being configured to press the workpiece against the
polishing surface; a sensor provided on the polishing table and
configured to monitor a surface state of the workpiece during
polishing of the workpiece; and a monitoring device configured to
process signal from the sensor. A rotational speed of the top ring
and a rotational speed of the polishing table are set such that the
sensor travels across a surface of the workpiece in a different
path every time the sensor scans the surface of the workpiece, and
the monitoring device is configured to calculate an average of
signal values obtained along plural paths of the sensor which
rotate around the surface of the workpiece and provide a set of
sensor paths.
[0044] According to the present invention, by adjusting the
rotational speed of the polishing table and the rotational speed of
the top ring, the sensor does not scan only local areas, but scans
substantially the entire surface of the workpiece evenly in the
predetermined measuring time. As a result, an average film
thickness can be grasped while an influence of noise is suppressed.
Therefore, an accurate polishing end point detection and uniform
film thickness can be realized.
BRIEF DESCRIPTION OF DRAWINGS
[0045] FIG. 1 is a schematic view showing an overall arrangement of
a polishing apparatus capable of performing a method of detecting a
polishing end point according to an embodiment of the present
invention;
[0046] FIG. 2 is a diagram showing the operation of light-receiving
elements in a spectroscope unit in a case where a pulsed light
source is used in the polishing state monitoring apparatus shown in
FIG. 1;
[0047] FIG. 3 is a diagram showing the operation of light-receiving
elements in a spectroscope unit in a case where a continuous light
source is used in the polishing state monitoring apparatus shown in
FIG. 1;
[0048] FIG. 4 is a plan view illustrative of sampling timings of
the polishing state monitoring apparatus shown in FIG. 1;
[0049] FIG. 5 is a cross-sectional view showing a sample substrate
having an oxide film formed on metal interconnects;
[0050] FIG. 6 is a graph showing spectral waveforms and reference
spectral waveforms;
[0051] FIG. 7 is a flow diagram illustrating calculation of a
characteristic value and selection of the wavelengths;
[0052] FIG. 8 is a graph showing a change in the characteristic
value with time;
[0053] FIG. 9 is a graph showing a weight function;
[0054] FIG. 10 is a graph showing the manner of change in a
distinctive point when shifting the selected two wavelengths to
longer wavelengths by 10 nm and to shorter wavelengths by 10
nm;
[0055] FIG. 11 is a schematic view showing a whole structure of a
polishing apparatus according to another embodiment of the present
invention;
[0056] FIG. 12 is a schematic view showing a cross section of the
top ring shown in FIG. 11;
[0057] FIG. 13 is a plan view showing a positional relationship
between a polishing table and a substrate;
[0058] FIG. 14 is a view showing paths of a sensor sweeping across
the substrate;
[0059] FIG. 15 is a plan view showing an example of selecting
measuring points to be monitored by a monitoring device among the
measuring points on the substrate shown in FIG. 14;
[0060] FIG. 16 is a graph showing the reflection intensity;
[0061] FIG. 17 is a view showing paths of the sensor described on
the substrate in a case where a rotational speed of the polishing
table is 70 min.sup.-1 and a rotational speed of the top ring 114
is 71 min.sup.-1;
[0062] FIG. 18 is a graph showing a signal waveform of the
characteristic value obtained under the conditions shown in FIG.
17;
[0063] FIG. 19 is a view showing the paths of the sensor described
on the substrate within a moving average time in the case where the
rotational speed of the polishing table is 70 min.sup.-1 and the
rotational speed of the top ring is 77 min.sup.-1;
[0064] FIG. 20 is a graph showing a signal waveform of the
characteristic value obtained under the conditions shown in FIG.
19;
[0065] FIG. 21 is a view showing the sensor paths on the substrate
while the polishing table makes ten revolutions under the same
conditions as those in FIG. 19;
[0066] FIG. 22 is a graph showing an example of a pre-polish
thickness and a post-polish thickness of a copper film, measured
along a circumferential direction, formed on a substrate having a
diameter of 300 mm;
[0067] FIG. 23 is a view showing the sensor paths on the surface of
the substrate when the rotational speed of the polishing table is
set to 60 min.sup.-1 and the rotational speed of the top ring is
set to 31 min.sup.-1;
[0068] FIG. 24 is a graph showing results of an operation example
in which pressures in four pressure chambers of the top ring are
operated during polishing so as to make the film thickness uniform
in zones C1, C2, C3, and C4 distributed along a radial direction of
the substrate W;
[0069] FIG. 25 is a view showing the sensor paths on the surface of
the substrate when the rotational speed of the polishing table is
adjusted to 60 min.sup.-1 and the rotational speed of the top ring
114 is adjusted to 36 min.sup.-1;
[0070] FIG. 26 is a graph showing changes in the pressures in the
pressure chambers of the top ring when polishing the substrate
under the conditions as shown in FIG. 25; and
[0071] FIG. 27 is a table showing examples of a ratio R/V of the
rotational speeds of the top ring and the polishing table which
satisfies an equation (9).
BEST MODE FOR CARRYING OUT THE INVENTION
[0072] Embodiments of the present invention will be described in
detail below with reference to the drawings.
[0073] FIG. 1 is a schematic view showing an overall arrangement of
a polishing apparatus capable of performing a method of detecting a
polishing end point according to an embodiment of the present
invention. As shown in FIG. 1, the polishing apparatus has a
polishing table 12 with a polishing pad 10 attached to an upper
surface thereof, and a top ring 14 for holding a substrate W, which
is a workpiece (object to be polished) and pressing the substrate W
against an upper surface of the polishing pad 10. The upper surface
of the polishing pad 10 serves as a polishing surface providing a
sliding contact with the substrate W. An upper surface of a fixed
abrasive plate containing fine abrasive particles (made of
CeO.sub.2 or the like) fixed by a binder, such as resin, may be
used as a polishing surface.
[0074] The polishing table 12 is coupled to a motor (not shown)
disposed therebelow, and is rotatable about its own axis as
indicated by arrow. A polishing liquid supply nozzle 16 is disposed
above the polishing table 12 and supplies a polishing liquid Q onto
the polishing pad 10.
[0075] The top ring 14 is coupled to a top ring shaft 18, which is
coupled to a motor and an elevating cylinder (not shown). The top
ring 14 can thus be vertically moved as indicated by arrow and
rotated about the top ring shaft 18. The substrate W as the object
of polishing is attracted to and held on a lower surface of the top
ring 14 by a vacuum suction or the like. With this arrangement, the
top ring 14 can press the substrate W held on its lower surface
against the polishing pad 10 at a desired pressure, while rotating
about its own axis.
[0076] In the polishing apparatus of the above construction, the
substrate W held on the lower surface of the top ring 14 is pressed
against the polishing pad 10 on the upper surface of the rotating
polishing table 12. The polishing liquid Q is supplied onto the
polishing pad 10 from the polishing liquid supply nozzle 16. The
substrate W is thus polished with the polishing liquid Q being
present between the surface (lower surface) of the substrate W and
the polishing pad 10.
[0077] The polishing table 12 has a polishing state monitoring
apparatus 20 embedded therein for monitoring a polishing state of
the substrate W during polishing of the substrate W. This polishing
state monitoring apparatus 20 is configured so as to monitor,
continuously in real-time, a polishing situation (a thickness and a
state of the remaining film) on the surface of the substrate W
during polishing of the substrate W. A light transmission unit 22
for transmitting light from the polishing state monitoring
apparatus 20 therethrough is attached to the polishing pad 10. The
light transmission unit 22 is made of a material of high
transmittance, e.g., non-foamed polyurethane or the like.
Alternatively, the light transmission unit 22 may be in the form of
a transparent liquid flowing upwardly into a through-hole that is
formed in the polishing pad 10. In this case, the liquid is
supplied into the through-hole while the through-hole is being
closed by the substrate W. The light transmission unit 22 may be
located in any position on the polishing table 12 as long as it can
travel across the surface of the substrate W held by the top ring
14. However, it is preferable that the light transmission unit 22
be located in a position where it passes through a center of the
substrate W.
[0078] As shown in FIG. 1, the polishing state monitoring apparatus
20 includes a light source 30, a light-emitting optical fiber 32
serving as a light-emitting unit for applying light from the light
source 30 to the surface of the substrate W, a light-receiving
optical fiber 34 serving as a light-receiving unit for receiving
reflected light from the surface the substrate, a spectroscope unit
36 having a spectroscope for dividing light received by the
light-receiving optical fiber 34 and a plurality of photodetectors
for converting the light, divided by the spectroscope, into
electrical information and storing the resultant electrical
information, a control unit 40 for controlling energization and
de-energization of the light source 30 and a timing to start a
reading process of the photodetectors of the spectroscope unit 36,
and a power supply 42 for supplying electric power to the control
unit 40. The light source 30 and the spectroscope unit 36 are
supplied with electric power through the control unit 40.
[0079] The light-emitting optical fiber 32 and the light-receiving
optical fiber 34 have a light-emitting end and a light-receiving
end, respectively, which are arranged to be substantially
perpendicular to the surface of the substrate W. The light-emitting
optical fiber 32 and the light-receiving optical fiber 34 are
arranged so as not to project upwardly from the surface of the
polishing table 12 in consideration of replacement work for the
polishing pad 10 and the quantity of light received by the
light-receiving optical fiber 34. The photodetectors of the
spectroscope unit 36 may comprise an array of 512 photodiodes.
[0080] The spectroscope unit 36 is coupled to the control unit 40
via a cable 44. The information from the photodetectors of the
spectroscope unit 36 is transmitted to the control unit 40 via the
cable 44. Based on the information, the control unit 40 generates
spectral data of the reflected light. Specifically, the control
unit 40 according to the present embodiment serves as a spectral
data generator configured to read the electrical information stored
in the photodetectors and generate spectral data of the reflected
light. A cable 46 extends from the control unit 40 through the
polishing table 12 to a processor 48, which is a personal computer,
for example. The spectral data generated by the spectral data
generator of the control unit 40 are transmitted to the processor
48 through the cable 46.
[0081] Based on the spectral data received from the control unit
40, the processor 48 calculates a characteristic value of the
surface of the substrate W. The characteristic value is an index
indicating a polishing state of the surface of the substrate. The
processor 48 also has a function to receive information as to
polishing conditions from a controller (not shown) which controls
the polishing apparatus, and a function to determine a polishing
end point (stop of polishing or a change of polishing conditions)
based on time variation of the calculated characteristic value and
send a command to the controller of the polishing apparatus.
[0082] As shown in FIG. 1, a proximity sensor 50 is mounted on a
lower end of the polishing table 12 in a position near its
circumferential edge, and a dog 52 is mounted outwardly of the
polishing table 12 in alignment with the proximity sensor 50. Each
time the polishing table 12 makes one revolution, the proximity
sensor 50 detects the dog 52 to thereby determine a rotation angle
of the polishing table 12.
[0083] The light source 30 comprises a light source configured to
emit light having a wavelength range including white light. For
example, a pulsed light source, such as a xenon lamp, can be used
as the light source 30. When the pulsed light source is used as the
light source 30, the light source 30 emits pulsed light at each
measuring point according to a trigger signal during a polishing
process. Alternatively, a tungsten lamp may be used as the light
source 30. In this case, the light source 30 may emit light
continuously at least when the light-emitting end of the
light-emitting optical fiber 32 and the light-receiving end of the
light-receiving optical fiber 34 are facing the surface of the
substrate W.
[0084] Light from the light source 30 travels through the
light-emitting end of the light-emitting optical fiber 32 and the
light transmission unit 22, and is applied to the surface of the
substrate W. The light is reflected off the surface, being
polished, of the substrate W, passes through the light transmission
unit 22, and is received by the light-receiving optical fiber 34 of
the polishing state monitoring apparatus. The light, received by
the light-receiving optical fiber 34, is transmitted to the
spectroscope unit 36, which divides the light into a plurality of
light rays according to wavelengths. The divided light rays having
respective wavelengths are applied to the photodetectors
corresponding to the wavelengths, and the photodetectors store
electric charges according to quantities of the light rays applied.
The electrical information stored in the photodetectors is read
(released) at a predetermined timing, and converted into a digital
signal. The digital signal is sent to the spectral data generator
of the control unit 40, and the control unit 40 generates spectral
data corresponding to respective measuring points.
[0085] Operation of the photodetectors of the spectroscope unit 36
will be described below. FIGS. 2 and 3 are diagrams showing an
operating manner of the photodetectors in a case where the
spectroscope unit 36 has photodetectors 60-1 through 60-N (the
total number is N). More specifically, FIG. 2 shows a case where
the pulsed light source is used as the light source 30, and FIG. 3
shows a case where the continuous light source is used as the light
source 30. In FIGS. 2 and 3, horizontal axis represents time, and
rising portions of graphs show that the electrical information is
stored in the photodetectors, and falling portions show that the
electrical information is read (released) from the photodetectors.
In FIG. 2, black circles ( ) indicate times when the pulsed light
source is turned on.
[0086] In one sampling cycle, the photodetectors 60-1 through 60-N
are successively switched from one to another to read (release) the
electrical information therefrom. As described above, the
photodetectors 60-1 through 60-N store the quantities of light rays
of the corresponding wavelengths as the electrical information, and
the stored electrical information is repeatedly read (released)
from the photodetectors 60-1 through 60-N at a sampling period T
with phase difference therebetween. The sampling period T is set to
be relatively small, insofar as sufficient quantities of light are
stored as electrical information in the photodetectors 60-1 through
60-N and data read from the photodetectors 60-1 through 60-N can
sufficiently be processed in real-time. When an array of 512
photodiodes is used as the photodetectors, the sampling period T is
on the order of 10 milliseconds. In FIGS. 2 and 3, S represents a
time from when the first photodetector 60-1 is read to when the
last photodetector 60-N is read, where S<T. In the case of FIG.
2, the time (indicated by in FIG. 2) when the pulsed light source
is turned on is a sampling time. In the case of FIG. 3, the time
(indicated by "x" in FIG. 3) that is half the time after the first
photodetector 60-1 is read and starts storing new electrical
information until the last photodetector 60-N is read is a sampling
time for corresponding measuring areas. Points on the substrate W
which face the light transmission unit 22 at the sampling times
will be referred to as sampling points.
[0087] In FIG. 2, all the photodetectors 60-1 through 60-N store
light while the light source 30 lights up instantaneously (for
about several microseconds). Where Q represents the time from when
the electrical information stored in the last photodetector 60-N is
read (released) to when the light source 30 is turned on, if the
light source 30 is tuned on before the electrical information
stored in the first photodetector 60-1 is read (released), an
inequality 0<Q<T-S holds. While Q can take any value within
the range indicated by the above inequality, the following
descriptions use a value of Q=(T-S)/2. The first photodetector 60-1
is read and starts storing new electrical information at a timing
that is earlier than the sampling time by S+Q, i.e., (T+S)/2. In
FIG. 3, the first photodetector 60-1 is also read at a timing that
is earlier than the sampling time by (T+S)/2. With respect to the
continuous light source shown in FIG. 3, the photodetectors 60-1
through 60-N start storing electrical information at different
times, and the stored electrical information is read from the
photodetectors 60-1 through 60-N at different times. Consequently,
actual measuring areas slightly vary depending on the
wavelengths.
[0088] Next, processes of determining a sampling timing by the
polishing state monitoring apparatus 20 will be described. First, a
process of determining a sampling timing in a case of using the
pulsed light source will be described. FIG. 4 is a view
illustrative of sampling timings of the polishing state monitoring
apparatus 20. Each time the polishing table 12 makes one
revolution, the proximity sensor 50 disposed on the circumferential
edge of the polishing table 12 detects the dog 52 which serves as a
reference position for operation of the proximity sensor 50.
Specifically, as shown in FIG. 4, a rotation angle is defined as an
angle, in a direction opposite to a direction of rotation of the
polishing table 12, from a line L.sub.T-W (hereinafter referred to
as a substrate center line) that interconnects the center C.sub.T
of rotation of the polishing table 12 and the center C.sub.W of the
substrate W. The proximity sensor 50 detects the dog 52 when the
rotation angle is .theta.. The center C.sub.W of the substrate W
can be specified by controlling the position of the top ring
14.
[0089] As shown in FIG. 4, where a horizontal distance between the
center C.sub.T of the polishing table 12 and the center C.sub.L of
the light transmission unit 22 is represented by L, a horizontal
distance between the center C.sub.T of the polishing table 12 and
the center C.sub.W of the substrate W is represented by M, a radius
of a measuring target surface of the substrate W which is the
surface, to be polished, of the substrate W excluding an edge cut
region thereof is represented by R, and an angle at which the light
transmission unit 22 scans the measuring target surface of the
substrate W is represented by 2.alpha., the following equation (1)
holds based on the cosine theorem, and the angle .alpha. can be
determined from the following equation (1).
.alpha. = cos - 1 ( L 2 + M 2 - R 2 2 LM ) ( 1 ) ##EQU00001##
[0090] In the present embodiment, sampling timings are adjusted
such that a point P on the substrate center line L.sub.T-W through
which the light transmission unit 22 passes is always selected as a
sampling point. Where the number of sampling points on one side of
the substrate center line L.sub.T-W is n (which is an integer), the
number of all sampling points when the light transmission unit 22
scans the measuring target surface of the substrate W is expressed
by 2n+1, including the sampling point P on the substrate center
line L.sub.T-W.
[0091] If a circumferential portion of the top ring 14 is located
outwardly of the substrate W so as to block background light, the
condition for the light transmission unit 22 to be present within
the measuring target surface of the substrate W at a first sampling
time can be expressed by the following inequality (2), where COT
represents an angular velocity of the polishing table 12. The
integer n which satisfies this condition can be obtained from the
following inequality (2).
.alpha.-.omega..sub.TT.ltoreq.n.omega..sub.TT<.alpha.
That is,
.alpha. .omega. T T - 1 .ltoreq. n < .alpha. .omega. T T ( 2 )
##EQU00002##
[0092] If the light transmission unit 22 and the proximity sensor
50 are located at the same angle with respect to the center C.sub.T
of the polishing table 12, a time t.sub.s from when the proximity
sensor 50 detects the dog 52 to when the first photodetector 60-1
starts storing electrical information in the first sampling cycle
while the polishing table 12 makes one revolution, i.e., a sampling
start time t.sub.s, can be determined from the following equation
(3).
t S = .theta. .omega. T - ( nT + T + S 2 ) = .theta. .omega. T - (
n + 1 2 ) T - S 2 ( 3 ) ##EQU00003##
[0093] In order to reliably clear the quantity of light stored in
the photodetectors while the light transmission unit 22 is located
outside of the surface, being polished, of the substrate W, the
data acquired in the first sampling cycle may be discarded. In this
case, the sampling start time t.sub.s can be determined from the
following equation (4).
t S = .theta. .omega. T - ( nT + T + S 2 + T ) = .theta. .omega. T
- ( n + 3 2 ) T - S 2 ( 4 ) ##EQU00004##
[0094] The polishing state monitoring apparatus 20 starts its
sampling operation based on the sampling start time t.sub.s thus
determined. Specifically, the control unit 40 starts pulse lighting
of the light source 30 after elapse of the time t.sub.s from the
detection of the dog 52 by the proximity sensor 50, and controls
the operation timing of the photodetectors of the spectroscope unit
36 so as to repeat a sampling operation on a cycle of the sampling
period T. Reflection spectral data at each sampling point are
generated by the spectral data generator of the control unit 40 and
is transmitted to the processor 48. Based on the spectral data, the
processor 48 determines a characteristic value of the surface,
being polished, of the substrate W.
[0095] In the present embodiment, since the point P on the
substrate center line L.sub.T-W which is on the path of the light
transmission unit 22 is always selected as a sampling point, the
characteristic value at a given radial position on the surface of
the substrate can repeatedly be measured each time the polishing
table 12 makes one revolution. If the sampling period is constant,
then the radial positions of measuring points on the surface of the
substrate per revolution of the polishing table 12 become constant.
Therefore, this measuring process is more advantageous in
recognizing the situation of a remaining film on the substrate W
than the case where the characteristic values at unspecific
positions are measured. In particular, if the light transmission
unit 22 is arranged so as to pass through the center C.sub.W of the
substrate W, then the center C.sub.W of the substrate W is always
measured as a fixed point each time the polishing table 12 makes
one revolution. Therefore, a more accurate grasp of a time
variation of a remaining film situation of the substrate W can be
realized.
[0096] If the continuous light source is used as the light source
30, since the respective photodetectors continuously store
electrical information and start storing the electrical information
at different times, the integer n is determined in a manner
different from a pulsed light source. Specifically, when the first
photodetector 60-1 starts storing electrical information, the light
transmission unit 22 needs to be present in the measuring target
surface of the substrate W. Therefore, the inequality for
determining the integer n is given as follows.
.alpha.-.omega..sub.TT.ltoreq.n.omega..sub.TT+.omega..sub.T2/T+S<.alp-
ha.
That is,
( .alpha. .omega. T - S 2 ) T - 3 2 .ltoreq. n < ( .alpha.
.omega. T - S 2 ) T - 1 2 ( 5 ) ##EQU00005##
[0097] The integer n can be determined from the above inequality
(5), and the sampling start time t.sub.s can be determined based on
the equation (3) or (4). As well as the case of using the pulsed
light source, the polishing state monitoring apparatus 20 starts
its sampling process based on the determined sampling start time
t.sub.s, and determines a characteristic value of the surface,
being polished, of the substrate W from spectral data at each
sampling point. In the above example, certain conditions are
established with respect to the timing of lighting the pulsed light
source and the positional relationship between the light
transmission unit 22 and the proximity sensor 50. Even if these
conditions are not met, n and t.sub.s can similarly be
determined.
[0098] Next, a method of detecting a polishing end point from the
spectral data at each sampling point will be described. FIG. 5 is a
cross-sectional view showing a substrate (a reference workpiece)
having an oxide film formed on metal interconnects. In this
example, the oxide film 80 on the metal interconnects 70 is
polished by a thickness of 800 nm (for 104 seconds), and reflection
intensity during this polishing process is obtained as sample data.
In FIG. 5, a target polishing end point is set to a time of 94
seconds. Reference numeral 100 in FIG. 6 represents a spectral
waveform obtained at the time of 94 seconds. Reference numeral 100a
and reference numeral 100b represent spectral waveforms each
obtained at a polishing time other than the time of 94 seconds. A
difference in shape between the spectral waveforms 100, 100a, and
100b indicates a difference in polishing time (i.e., a difference
in film thickness). However, due to influences of device patterns
or materials of underlying films, a basic shape of each spectral
waveform is distorted greatly. This makes it difficult to recognize
characteristics of a change in the reflection intensity as a result
of a change in film thickness.
[0099] Thus, in order to remove the distortion of the basic shape
of the spectral waveform, the spectral waveform 100 at the target
film thickness (i.e., the polishing end point) of the reference
workpiece is divided by reflection intensity averages, each of
which is an average of reflection intensities at each wavelength
within a polishing time, so that a reference spectral waveform is
created. More specifically, the reflection intensities at each
wavelength are averaged over the polishing time (in this example, 0
to 104 seconds), so that an average reflection intensity for each
wavelength is determined. Then, each of the reflection intensities,
indicated by the spectral waveform 100, is divided by the
corresponding average reflection intensity at each wavelength,
whereby the reference spectral waveform is obtained. In FIG. 6, a
right vertical axis indicates a magnitude of the reference spectral
waveform. Reference spectral waveforms 200, 200a, and 200b
correspond to the spectral waveforms 100, 100a, and 100b. As can be
seen from FIG. 6, compared with the spectral waveforms prior to
normalization, the reference spectral waveforms have clearly
distinguishable shapes reflecting the difference in film thickness.
Moreover, local maximum points and local minimum points appear
clearly. Thus, based on the reference spectral waveform 200 at the
target film thickness, wavelengths of a local maximum value and a
local minimum value are selected, and the characteristic value as
an index of the film thickness is calculated from a combination of
reflection intensities at the selected wavelengths. While each of
the reflection intensities is divided by the corresponding average
reflection intensity at each wavelength in this embodiment, the
same result can also be obtained by subtracting each of the average
reflection intensities from the corresponding reflection intensity
at each wavelength. If the spectral waveform is not distorted, the
local maximum point and the local minimum point may be determined
from the spectral waveform, without creating the reference spectral
waveforms.
[0100] Next, the calculation of the characteristic value and the
selection of the wavelengths will be described with reference to a
flow diagram as shown in FIG. 7. First, the substrate (the
reference workpiece) having pattern interconnects as shown in FIG.
5 is polished until the target film thickness is reached, and the
film thickness is measured. Subsequently, two wavelengths of a
local maximum value and a local minimum value are selected based on
the reference spectral waveform of the polished substrate. Then,
the characteristic value is determined from the reflection
intensities at the selected two wavelengths. If necessary, the
wavelengths to be selected may be shifted to longer wavelengths or
shorter wavelengths so that fine adjustment of the characteristic
value is made (this will be described in detail later). Next, a
substrate identical to the reference workpiece is polished. From
the results of polishing of this substrate, whether or not the
characteristic value shows a distinctive point, i.e., whether or
not the target film thickness can be detected by monitoring the
time variation of the characteristic value is verified. If the
target film thickness can be detected, the above-mentioned
distinctive point is set as a polishing end point, and is used in
the polishing end point detection in polishing of other substrates.
These processes are performed in the processor 48.
[0101] The process of determining the characteristic value will be
described with reference to a specific example. As shown in FIG. 6,
a wavelength of 540 nm at which the reference spectral waveform 200
takes a local maximum value and a wavelength of 576 nm at which the
reference spectral waveform 200 takes a local minimum value are
selected. Then, a characteristic value X(t) is determined from the
following equation.
X(t)=.rho..sub.540(t)/(.rho..sub.540(t)+.rho..sub.576(t)) (6)
[0102] In the above equation, .rho. represents a reflection
intensity and t represents a polishing time.
[0103] This characteristic value X(t) is used in polishing of a
next substrate or a substrate to be polished after an arbitrary
number of substrates are polished.
[0104] The above description is about the process of calculating
the characteristic value from the reference spectral waveform of
the reference workpiece. In another example, an average of the
reflection intensities at each wavelength over the polishing time
of the reference workpiece, may be used in a polishing process of a
next substrate or a substrate to be polished after an arbitrary
number of substrates are polished. Specifically, the reflection
intensity, obtained in currently performed polishing of a
substrate, is divided by the average of the refection intensities
of the reference workpiece at each wavelength, so that a reference
spectral waveform is obtained. This reference spectral waveform is
monitored during polishing of the substrate in the same manner as
described above, so that the polishing end point is determined
based on the reference spectral waveform. As described above, since
the reference spectral waveform has a distinguishable shape, an
accurate polishing end point detection can be realized.
[0105] FIG. 8 is a graph showing a change with time in the
characteristic value determined from the above-described equation
(6). As can be seen from FIG. 8, a local maximum value of the
characteristic value appears at a time of 94 seconds as intended.
Therefore, this distinctive point at which the local maximum value
appears is preset as a polishing end point, and a polishing process
is terminated when the distinctive point is detected. After the
detection of the distinctive point, a substrate may be
over-polished for a predetermined period of time. As shown in FIG.
8, an initial stage of polishing in first 20 seconds is in a
process of removing irregularities from a substrate. Therefore, the
characteristic value is noisy and has fine extrema. Thus, the
polishing end point detection may be such that monitoring of the
characteristic value is started after an elapse of 25 seconds from
a polishing start point and a polishing end point is determined
when a fifth local maximum value, in this example, is detected.
[0106] When wavelengths of a largest local maximum value and a
smallest local minimum value are selected as extremum wavelengths
for determining the characteristic value, the characteristic value
tends to fluctuate greatly. As a result, a good signal-to-noise
ratio is obtained in most cases. However, depending on device
structures, selection of the wavelengths of the largest local
maximum value and the smallest local minimum value may not bring a
best result. Thus, it is preferable to select several combinations
of wavelengths from among plural extremum wavelengths, observe a
shape of the characteristic value determined from each combination,
and select extremum wavelengths which are such that a distinctive
point appears clearly at a target film thickness. While two
extremum wavelengths are extracted for determining the
characteristic value in the above example, any number of extremum
wavelengths can be extracted from among the extremum wavelengths
obtained. Possible combinations of extremum wavelengths include
.rho..sub.k/.rho..sub.i and (.rho..sub.j+ . . .
+.rho..sub.j+q)/(.rho..sub.i+ . . . +.rho..sub.i+p).
[0107] In the above-described example, the characteristic value is
calculated based on the time variation of the reflection
intensities at the selected extremum wavelengths. Alternatively, as
described in Japanese laid-open patent publication No. 2004-154928
(patent application No. 2003-321639), it is possible to determine
the characteristic value by multiplying a weight function having a
weight centered on the extremum wavelength by the spectral
waveform. Normal distribution may be used as a shape of the weight
function. The method of using such weight function will be
described below.
[0108] First, a wavelength .lamda.=540 nm, which shows a local
maximum value, is selected based on the reference spectral waveform
200 at the polishing end point. Next, as shown in FIG. 9, a weight
function w(.lamda.) having a weight centered on this wavelength
(540 nm) is defined in advance. Measurements .rho.(.lamda.) of
reflection intensity of the reflected light from the surface of the
substrate are multiplied by the weight function w(.lamda.), and the
resultant values are added, i.e., integrated into a scalar value.
The resultant scalar value is defined as a characteristic value X.
Specifically, the characteristic value X is defined according to
the following equation (7).
X = .lamda. w ( .lamda. ) .rho. ( .lamda. ) .DELTA..lamda. ( 7 )
##EQU00006##
[0109] Alternatively, plural weight functions w.sub.i(.lamda.)
(i=1, 2, . . . ) may be defined, and the characteristic value
X.sub.i may be defined according to the following equation (8).
X i = .lamda. w i ( .lamda. ) .rho. ( .lamda. ) .DELTA..lamda. i
.lamda. w i ( .lamda. ) .rho. ( .lamda. ) .DELTA..lamda. ( 8 )
##EQU00007##
[0110] According to the method as described above, when a target
film thickness is reached, i.e., when the polishing end point is
reached, the characteristic value shows a distinctive changing
point (distinctive point) such as a local maximum or a local
minimum. Therefore, by monitoring the characteristic value during
polishing and detecting the distinctive point of time variation of
the characteristic value, the polishing end point (e.g., polishing
stop point or a changing point of polishing conditions) can be
determined. Further, according to the method as described above,
even if a disturbance affects measurements of the reflection
intensity at a certain wavelength, the influence of the disturbance
is reduced because of the integration operation, compared with the
case where the reflection intensity at the target film thickness is
directly monitored.
[0111] The polishing end point detection method according to this
embodiment is advantageous over the method disclosed in the
Japanese laid-open patent publication No. 2004-154928 in the
following respects. In the method of the patent publication No.
2004-154928, selection of a weight function that brings a
distinctive change in the characteristic value at the target film
thickness (i.e., the polishing end point) entails trial and error,
which necessitate a lot of time. In addition, some weight functions
may result in a bad SN ratio (signal-to-noise ratio), causing
failure in a stable polishing end point detection. Furthermore,
even when a film material to be polished and a film thickness are
the same, the spectral waveform of the reflected light is affected
by the difference in device pattern, type of underlying film, and
device structure. In order to obtain a good result, it is necessary
to define an optimum weight function for every different type of
substrate, and as a result a productivity is lowered. According to
the present embodiment, the reference spectral waveform having
characteristic extrema can be obtained by dividing the reflection
intensities by the average reflection intensities, and an optimum
weight function can be easily determined.
[0112] Excessive noise due to device patterns may cause not only
the pre-normalization spectral waveform but also the distinctive
point of the characteristic value, obtained from the normalized
spectral waveform, to deviate from the target film thickness (i.e.,
the target polishing end time). In such a case, times of the
extrema of the characteristic value can be adjusted by shifting the
extremum wavelengths of the spectral waveform selected for
calculation of the characteristic value. Therefore, it is
preferable to reselect optimum wavelengths indicating a distinctive
point at the polishing end point. When shifting the selected two
wavelengths to longer wavelengths, an appearance time of the
distinctive point of the characteristic value is shifted to shorter
polishing times (i.e., larger film thicknesses). On the other hand,
when shifting the selected two wavelengths to shorter wavelengths,
an appearance time of the distinctive point of the characteristic
value is shifted to longer polishing times (i.e., smaller film
thicknesses). FIG. 10 is a graph showing the manner of change in
the distinctive point when shifting the selected two wavelengths to
longer wavelengths by 10 nm and to shorter wavelengths by 10 nm.
According to the above-described way of determining the wavelengths
for an approximate polishing end point, the distinctive point of
the characteristic value is easily matched to the polishing end
point by fine adjustment of the selected wavelengths.
[0113] If a distinctive point of a change in the reflection
intensity as a result of a change in the film thickness can be
captured from the pre-normalization spectral waveform, the
characteristic value can be determined from the wavelengths at
which the pre-normalization spectral waveform has extrema. In a
case where devices have a simple structure, a spectral waveform may
be obtained from simulation calculation, as long as the simulation
calculation can produce a satisfactory waveform at a predetermined
film thickness from a practical standpoint.
[0114] As described above, according to the embodiment of the
present invention, it is possible to obtain the characteristic
value which has a distinctive changing point at the polishing end
point and has a good signal-to-noise ratio depending on a device
pattern of a substrate. Therefore, an accurate polishing end point
can be detected. The above-described embodiment can be applied not
only to a polishing method and a polishing apparatus, but also to a
method and apparatus for etching away a film to a target thickness
and a method and apparatus for forming a film to a target
thickness.
[0115] Next, another embodiment of the present invention will be
described.
[0116] FIG. 11 is a schematic view showing a whole structure of a
polishing apparatus according to another embodiment of the present
invention. As shown in FIG. 11, the polishing apparatus has a
polishing table 112 supporting a polishing pad 110 attached to an
upper surface thereof, and a top ring 114 configured to hold a
substrate, which is a workpiece to be polished, and to press the
substrate against an upper surface of the polishing pad 110. The
upper surface of the polishing pad 110 provides a polishing surface
with which the substrate is brought into sliding contact.
[0117] The polishing table 112 is coupled to a motor (not shown in
the drawing) disposed therebelow, and is rotatable about its own
axis as indicated by arrow. A polishing liquid supply nozzle (not
shown in the drawing) is disposed above the polishing table 112, so
that a polishing liquid is supplied from the polishing liquid
supply nozzle onto the polishing pad 110.
[0118] The top ring 114 is coupled to a top ring shaft 118, which
is coupled to a motor and an elevating cylinder (not shown in the
drawing). The top ring 114 can thus be vertically moved and rotated
about the top ring shaft 118. The substrate to be polished is
attracted to and held on a lower surface of the top ring 114 by a
vacuum suction or the like.
[0119] With the above-described structures, the substrate, held on
the lower surface of the top ring 114, is rotated and pressed by
the top ring 114 against the polishing surface of the polishing pad
110 on the rotating polishing table 112. The polishing liquid is
supplied from the polishing liquid supply nozzle onto the polishing
surface of the polishing pad 110. The substrate is polished in the
presence of the polishing liquid between the surface (lower
surface) of the substrate and the polishing pad 110.
[0120] FIG. 12 is a schematic view showing a cross section of the
top ring shown in FIG. 11. As shown in FIG. 12, the top ring 114
has a disk-shaped top ring body 131 coupled to a lower end of the
top ring shaft 118 via a flexible joint 130, and a retainer ring
132 provided on a lower portion of the top ring body 131. The top
ring body 131 is made of a material having high strength and
rigidity, such as metal or ceramic. The retainer ring 132 is made
of highly rigid resin, ceramic, or the like. The retainer ring 132
may be formed integrally with the top ring body 131.
[0121] The top ring body 131 and the retainer ring 132 form therein
a space, which houses an elastic pad 133 which is to be brought
into contact with the substrate W, an annular pressure sheet 34
made from an elastic membrane, and a substantially disk-shaped
chucking plate 135 configured to hold the elastic pad 133. The
elastic pad 133 has an upper peripheral edge, which is held by the
chucking plate 135. Four pressure chambers (air bags) P1, P2, P3,
and P4 are provided between the elastic pad 133 and the chucking
plate 135. A pressurized fluid (e.g., a pressurized air) is
supplied into the pressure chambers P1, P2, P3, and P4 or a vacuum
is developed in the pressure chambers P1, P2, P3, and P4 via fluid
passages 137, 138, 139, and 140, respectively. The center pressure
chamber P1 has a circular shape, and the other pressure chambers
P2, P3, and P4 have an annular shape. These pressure chambers P1,
P2, P3, and P4 are in a concentric arrangement.
[0122] A pressure-adjusting device (not shown in the drawing) is
provided so as to change internal pressures of the pressure
chambers P1, P2, P3, and P4 independently of each other to thereby
substantially independently adjust pressing forces to be applied to
four zones: a central zone C1, an inner middle zone C2, an outer
middle zone C3, and a peripheral zone C4 (To be exact, each zone is
more or less affected by the pressure chamber corresponding to the
other zone, e.g., the adjacent zone). Further, by elevating or
lowering the top ring 114 in its entirety, the retainer ring 132
can be pressed against the polishing pad 110 at a predetermined
pressing force. A pressure chamber P5 is formed between the
chucking plate 135 and the top ring body 131. A pressurized fluid
is supplied into the pressure chamber P5 or a vacuum is developed
in the pressure chamber P5 via a fluid passage 141. With this
operation, the chucking plate 135 and the elastic pad 133 in their
entirety can be moved vertically.
[0123] The retainer ring 132 is arranged around the substrate W so
as to prevent the substrate W from coming off the top ring 114
during polishing.
[0124] As shown in FIG. 11, a sensor 150 for monitoring (i.e.,
detecting) a state of a film of the substrate W is provided in the
polishing table 112. This sensor 150 is coupled to a monitoring
device 153, which is couple to a CMP controller 154. An eddy
current sensor can be used as the sensor 150. An output signal of
the sensor 150 is sent to the monitoring device 153. This
monitoring device 153 performs necessary conversions and processing
(calculations) on the output signal (sensing signal) of the sensor
150 to produce a monitoring signal. While a value of the monitoring
signal (and the sensor signal) does not indicate a film thickness
itself, the value of the monitoring signal changes according to the
film thickness.
[0125] The monitoring device 153 also functions as a controller for
operating the internal pressures of the pressure chambers P1, P2,
P3, and P4 based on the monitoring signal, and also functions as a
polishing end point detector for detecting a polishing end point.
Specifically, the monitoring device 153 determines the pressing
forces of the top ring 114 against the substrate W based on the
monitoring signal. The determined pressing forces are sent to the
CMP controller 154. The CMP controller 154 commands the
non-illustrate pressure-adjusting device to change the pressing
forces of the top ring 114 against the substrate W. The monitoring
device 153 and the CMP controller 154 may be integrated into a
single control device.
[0126] FIG. 13 is a plan view showing a positional relationship
between the polishing table 112 and the substrate W. As shown in
FIG. 13, the sensor 150 is arranged in a location such that the
sensor 150 passes through a center C.sub.W of the substrate W, held
by the top ring 114, during polishing. A symbol C.sub.T is a center
of rotation of the polishing table 112. While moving under the
substrate W, the sensor 150 measures a thickness of a conductive
film (e.g., a Cu layer) or a quantity that increases or decreases
in accordance with a change in film thickness. The sensor 150
obtains measurements continuously along a path of its movement
(i.e., a scan line).
[0127] FIG. 14 is a view showing paths of the sensor 150 sweeping
across the substrate W. The sensor 150 scans the surface (that is
being polished) of the substrate W each time the polishing table
112 makes one revolution. Specifically, when the polishing table
112 is being rotated, the sensor 150 sweeps across the surface of
the substrate W in a path passing through the center C.sub.W of the
substrate W (center of the top ring shaft 118). A rotational speed
of the top ring 114 is generally different from a rotational speed
of the polishing table 112. Therefore, the path of the sensor 150
described on the surface of the substrate W changes as the
polishing table 112 rotates, as indicated by scan lines SL.sub.1,
SL.sub.2, SL.sub.3, . . . in FIG. 14. Even in this case, since the
sensor 150 is located so as to pass through the center C.sub.W of
the substrate W as described above, the path of the sensor 150
passes through the center C.sub.W of the substrate W in every
rotation. In this embodiment, measuring timings of the sensor 150
are adjusted so that the film thickness at the center C.sub.W of
the substrate W is always measured by the sensor 150 in every
rotation.
[0128] It is known that a polishing-rate profile of the substrate W
is substantially axisymmetric with respect to an axis that extends
through the center C.sub.W of the substrate W in a direction
perpendicular to the surface of substrate W. Accordingly, as shown
in FIG. 14, where an n-th measuring point on an m-th scan line
SL.sub.m is represented by MP.sub.m-n, the change in the film
thickness of the substrate W at n-th measuring points, which define
a radial position, can be monitored by tracking the monitoring
signals obtained at the n-th measuring points MP.sub.1-n,
MP.sub.2-n, . . . , MP.sub.m-n on respective scan lines.
[0129] In FIG. 14, for the sake of simplification, the number of
measuring points in one scanning operation is set to 15. However,
the number of measuring points is not limited to the illustrated
example and various numbers can be set in accordance with a period
of measuring operation and the rotational speed of the polishing
table 112. When using an eddy current sensor as the sensor 150, no
less than one hundreds of measuring points are generally set on one
scan line. When a large number of measuring points are set in this
manner, one of them substantially coincides with the center C.sub.W
of the substrate W. Therefore, it is not necessary in this case to
adjust the measuring timings with respect to the center C.sub.W of
the substrate W.
[0130] FIG. 15 is a plan view showing an example of selecting the
measuring points to be monitored by the monitoring device 153,
among the measuring points on the substrate W shown in FIG. 14. In
the example shown in FIG. 15, the monitoring device 153 monitors
the measuring points MP.sub.m-1, MP.sub.m-2, MP.sub.m-3,
MP.sub.m-4, MP.sub.m-5, MP.sub.m-6, MP.sub.m-8, MP.sub.m-10,
MP.sub.m-11, MP.sub.m-12, MP.sub.m-13, MP.sub.m-14, and MP.sub.m-15
located near centers and boundaries of the zones C1, C2, C3, and C4
to which the pressing forces are applied independently. An
additional measuring point may be provided between the measuring
points MP.sub.m-i and M.sub.m(i+1), unlike the example shown in
FIG. 14. Selecting of the measuring points to be monitored is not
limited to the example shown in FIG. 15. Any point to be observed
in view of polishing control of the surface of the substrate W can
be selected as the measuring point to be monitored. All of the
measuring points on each scan line can be selected.
[0131] The monitoring device 153 performs predetermined
calculations on the output signal (sensing signal) of the sensor
150 obtained at the selected measuring points to produce the
monitoring signals. Based on the monitoring signals and
below-described reference signal, the monitoring device 153
calculates the internal pressures of the pressure chambers P1, P2,
P3, and P4 in the top ring 114 corresponding to the respective
zones C1, C2, C3, and C4. More specifically, the monitoring device
153 compares the monitoring signals, obtained at the selected
measuring points, with the preset reference signal, and calculates
optimum pressures in the pressure chambers P1, P2, P3, and P4 that
can allow the respective monitoring signals to converge on the
reference signal. The calculated pressure values are sent from the
monitoring device 153 to the CMP controller 154, and the CMP
controller 154 changes the pressures in the pressure chambers P1,
P2, P3, and P4. In this manner, the pressing forces against the
respective zones C1, C2, C3, and C4 of the substrate W are
adjusted.
[0132] In order to eliminate noises so as to smoothen data, an
average of the monitoring signals, obtained at neighboring
measuring points, may be used. Alternatively, it is possible to
calculate an average or a representative value of the monitoring
signals obtained at the measuring points in each of the concentric
zones which are divided according to the radial position from the
center C.sub.W of the surface of the substrate W. In this case, the
average or representative value can be used as a new monitoring
signal for control. A distance of each measuring point from the
center C.sub.W of the substrate W may be determined at each point
of time during polishing, so that each measuring point is assigned
to the proper zone based on the distance from the center C.sub.W of
the substrate W. This operation is effective in a case where plural
sensors are arranged along the radial direction of the polishing
table 112 and in a case where the top ring 114 is configured to
swing around the top ring head shaft 118.
[0133] Next, a method of determining a polishing end point from the
reflection intensities obtained at the respective measuring points
using an optical sensor as the sensor 150 will be described based
on the description of the Japanese laid-open patent publication No.
2004-154928.
[0134] Where a film to be polished is a light-transmissive thin
film, such as an oxide film, with a uniform thickness and is in a
disturbance-free ideal state, time variation of relative
reflectances at respective wavelengths are as shown in FIG. 16
because of an interference caused by the film to be polished. Where
the film has a refractive index n and a film thickness d and light
has a wavelength .lamda. (in vacuum), a film thickness difference
corresponding to one period of the time variation is represented by
.DELTA.d=.lamda./2n. Therefore, as the film thickness decreases
linearly with the polishing time, the relative reflectance changes
with time such that its local maximum value and local minimum value
appear periodically, as shown in FIG. 16. In FIG. 16, a solid-line
represents a relative reflectance at a wavelength .lamda.=500 nm,
and the broken-line represents a relative reflectance at a
wavelength .lamda.=700 nm.
[0135] With regard to the characteristic value determined by
calculations including a multiplication that multiplies wavelength
components of spectral data by the weight function, the
characteristic value increases and decreases repetitively with the
polishing time, i.e., with the decrease in film thickness, in a
similar manner. In a case of pattern film, the characteristic value
increases and decreases repetitively as well, although noise or
distortion may appear on a waveform.
[0136] In monitoring of the characteristic value, the local maximum
value and/or local minimum value of time variation of the
characteristic value are detected, whereby the progress of
polishing is shown. If the polishing process is stopped at the time
an extremum is detected and the film thickness is measured as a
reference, the progress of polishing can be associated with the
thickness of the film being polished.
[0137] In detection of a polishing end point (stop point of
polishing or a point of changing polishing conditions), an extremum
(one of distinctive points) immediately before a desired film
thickness is reached is detected, and the film is over-polished for
a time which corresponds to the difference between the film
thickness at the extremum and the desired film thickness.
[0138] The reflection intensities measured at the measuring points
may be averaged each time the sensor 150 scans the surface of the
substrate W, and the above-described characteristic value may be
calculated from the resultant average. When the above-described
series of processes are performed on the reflection intensity data
for calculation of the characteristic value, it is preferable to
perform moving average at a desirable stage in processing of the
reflection intensity data. For example, it is possible to perform
moving average on the reflection intensity data and then perform
the above-described series of processes to determine the
characteristic value. Alternatively, it is possible to perform
moving average on the characteristic values calculated. Moving
average is a process to average time-series data obtained in a
predetermined time section (moving average time) while moving the
time section.
[0139] Next, a path (scan line) of the sensor 150 when sweeping
across the surface of the substrate will be described.
[0140] When the rotational speed of the polishing table and the
rotational speed of the top ring are the same, a relative speed is
the same at any point on the substrate, and the sensor, provided on
the polishing table, passes through the same zone of the substrate
every time the polishing table rotates. This is a
logically-established fact. The rotational speeds of the polishing
table and the top ring, however, cannot be exactly the same
actually. In addition, if the polishing table and the top ring
rotate at the same speed, the polishing table and the top ring are
synchronized and this synchronized rotation can cause insufficient
polishing in local zones due to an influence of grooves formed on
the polishing pad. For these reasons, it has been customary to
intentionally make a slight difference in rotational speed between
the polishing table and the top ring.
[0141] FIG. 17 is a view showing paths of the sensor 150 described
on the substrate W in a case where the rotational speed of the
polishing table 112 is 70 min.sup.-1 and the rotational speed of
the top ring 114 is 71 min.sup.-1.
[0142] Under these conditions, where the moving average time is set
to 5 seconds, the sensor 150 can scan the substrate W six times
during that period of time. In this case, the sensor path rotates
only by an angle of 5.14 degrees each time the polishing table 112
makes one revolution. As a result, information on only a local
portion of the substrate W is obtained, as shown in FIG. 17,
resulting in failure in grasp of an accurate change in the
reflection intensity with a change in film thickness.
[0143] FIG. 18 is a graph showing a signal waveform of the
characteristic value obtained under the conditions shown in FIG.
17. Generally, the characteristic value obtained from the
reflection intensity varies in a sine curve according to a change
in film thickness because of interference of light. However, in the
case where the rotational speed of the polishing table 112 is set
to 70 min.sup.-1, the rotational speed of the top ring 114 is set
to 71 min.sup.-1, and the moving average time is set to 5 seconds
(six points with respect to moving average point), random noise
appears on the signal waveform of the characteristic value, as
shown in FIG. 18. As described previously, the polishing end point
is generally determined based on detection of the local maximum
value or local minimum value of the characteristic value. However,
the extremum cannot be clearly captured due to the noise, or a time
of the extremum may be shifted from the original polishing end
time. In this case, an accurate polishing end point detection
cannot be performed.
[0144] Thus, in this invention, a ratio of the rotational speeds of
the top ring 114 and the polishing table 112 is adjusted such that
the paths of the sensor 150 described on the substrate W within a
predetermined period of time (e.g., within the moving average time)
are distributed substantially evenly over a circumference of the
surface of the substrate W in its entirety. FIG. 19 is a view
showing the paths of the sensor 150 described on the substrate
within the moving average time (5 seconds in this example) in the
case where the rotational speed of the polishing table 112 is 70
min.sup.-1 and the rotational speed of the top ring 114 is 77
min.sup.-1. As shown in FIG. 19, under these conditions, the path
of the sensor 150 rotates by 36 degrees each time the polishing
table 112 makes one revolution. Therefore, the path of the sensor
150 rotates by half of the circumference of the substrate W every
time the sensor 150 scans five times. In view of a curvature of the
sensor path, six-time sweep motions of the sensor 150 across the
substrate W within the moving average time allow the sensor 150 to
scan the entire surface of the substrate W substantially evenly.
Therefore, the influence of areas with different pattern densities
and different structures becomes substantially even in every moving
average time.
[0145] FIG. 20 is a graph showing a signal waveform of the
characteristic value obtained under the conditions shown in FIG.
19. As can be seen from FIG. 20, less noise appears on the signal
waveform of the characteristic value, compared with the case of
FIG. 18. If the moving average time is doubled, i.e., set to 10
seconds or if the rotational speed of the polishing table 112 is
set to 70 min.sup.-1 and the rotational speed of the top ring 114
is set to 84 min.sup.-1, the sensor path makes substantially one
revolution within the moving average time. Therefore, the accuracy
of the polishing end point detection can be further improved.
[0146] Generally, when the moving average process is performed on
time-series data, the processed data are obtained after a delay of
about half the moving average time with respect to actual data.
Further, if the ratio of the rotational speeds of the top ring 114
and the polishing table 112 is changed greatly, a distribution of
the relative speed between the top ring 114 and the polishing table
112 on the substrate W varies and as a result a film-thickness
profile of the substrate W is changed. Therefore, it is necessary
to determine the moving average time, the rotational speed of the
polishing table 112, and the rotational speed of the top ring 114
in consideration of permissible limits of a delay time depending on
a CMP process and a degree of the change in the film-thickness
profile. Generally, a slight change in the ratio of the rotational
speeds of the top ring 114 and the polishing table 112 hardly
affects the film-thickness profile. Therefore, it is easy to allow
the sensor 150 to scan the surface of the substrate W substantially
evenly only by adjustment of the ratio of the rotational speeds of
the top ring 114 and the polishing table 112.
[0147] While the rotational speed of the top ring 114 is higher
than the rotational speed of the polishing table 112 in the
above-described example, the rotational speed of the top ring 114
may be lower than the rotational speed of the polishing table 112
(for example, the rotational speed of the polishing table 112 may
be set to 70 min.sup.-1 and the rotational speed of the top ring
114 may be set to 63 min.sup.-1). In this case, the sensor path
rotates in the opposite direction, but the paths of the sensor 150
described on the surface of the substrate W within the
predetermined period of time are distributed over the entire
circumference of the surface of the substrate W as well as the
above example.
[0148] Further, while the ratio of the rotational speeds of the top
ring 114 and the polishing table 112 is close to 1 in the
above-described example, the ratio of the rotational speeds may be
close to 0.5, 1.5, or 2 (i.e., a multiple of 0.5). In this case
also, the same results can be obtained. For example, when the ratio
of the rotational speeds of the top ring 114 and the polishing
table 112 is set to 0.5, the sensor path rotates by 180 degrees
each time the polishing table 112 makes one revolution. When viewed
from the substrate W, the sensor 150 moves along the same path in
the opposite direction each time the polishing table 112 makes one
revolution.
[0149] The ratio of the rotational speeds of the top ring 114 and
the polishing table 112 may be slightly shifted from 0.5 (for
example, the rotational speed of the top ring 114 may be set to 36
min.sup.-1 and the rotational speed of the polishing table 112 may
be set to 70 min.sup.-1), so that the sensor path rotates by
180+.alpha. degrees each time the polishing table 112 makes one
revolution. In this case, the sensor path is shifted by an apparent
angle of .alpha. degree(s). Therefore, it is possible to establish
the value of .alpha. (i.e., the ratio of the rotational speeds of
the top ring 114 and the polishing table 112) such that the sensor
path rotates about 0.5 time, or about N time(s), or about 0.5+N
times (in other words, a multiple of 0.5, i.e., 0.5.times.N time(s)
(N is a natural number)) on the surface of the substrate W within
the moving average time.
[0150] This method of distributing the paths of the sensor 150 on
the surface of the substrate W substantially evenly over the
circumference of the substrate W in its entirety within the moving
average time can allow wide selection of the ratio of the
rotational speeds, in consideration of the adjustment of the moving
average time. Therefore, this method can be applied to a polishing
process which requires great variation of the ratio of the
rotational speeds of the top ring 114 and the polishing table 112
in accordance with polishing conditions such as characteristics of
a polishing liquid (slurry).
[0151] Generally, the path of the sensor 150 described on the
substrate W is curved as shown in FIG. 19, except in a case where
the rotational speed of the top ring 114 is just half the
rotational speed of the polishing table 112. Therefore, even when
the paths of the sensor 150 on the surface of the substrate W are
distributed over the entire circumference of the substrate W within
a predetermined time (e.g., the moving average time), these sensor
paths are not evenly distributed in the circumferential direction
of the substrate W in a strict sense. To exactly distribute the
sensor paths evenly in the circumferential direction of the
substrate W, it is necessary that the sensor path rotate just N
time(s) (N is a natural number) on the substrate W in every
predetermined period of time. During this period of time, the
sensor 150 scans the surface of the substrate W in directions or
orientations that are distributed evenly in the circumferential
direction of the substrate W over the entire circumference thereof.
To realize this, the rotational speeds of the polishing table 112
and the top ring 114 are determined such that, while the polishing
table 112 makes a predetermined number (natural number) of
revolutions, the top ring 114 makes just a predetermined number
(natural number) of revolutions that is different from the
predetermined number of revolutions of the polishing table 112. In
this case also, since the sensor paths are curved as described
above, it cannot be said that these paths are distributed at equal
intervals in the circumferential direction. However, supposing that
every two sensor paths make one pair, the sensor paths can be
regarded as being distributed evenly in the circumferential
direction at an arbitrary radial position FIG. 21 shows this
example. Specifically, FIG. 21 is a view showing the sensor paths
on the substrate W while the polishing table 112 makes ten
revolutions under the same conditions as those in FIG. 19. As can
be understood from the above description, the sensor 150 can obtain
data that more evenly reflect various structures of the entire
surface of the substrate W, compared with the above example.
[0152] Next, a specific example according to the above-described
principle will be described. In this example, a copper film is
prepared as an object of polishing and an eddy current sensor is
used as the sensor 150. A surface state of the substrate is
monitored by the sensor 150, and real-time control for adjusting a
distribution of pressing forces that press the substrate against
the polishing surface is performed so as to provide a uniform film
thickness with respect to the radial direction of the substrate. In
the previously-described embodiment in which the optical sensor is
used, all data obtained in one scanning operation can be averaged
for use in processing operations. In this example, such an
averaging process is not performed. Specifically, data indicating a
film thickness, which are obtained while the sensor 150 scans the
surface of the substrate W, are assigned to the zones C1, C2, C3,
and C4 (see FIG. 15) distributed in the radial direction of the
substrate W, and the data for the respective zones are used to
determine the pressures in the pressure chambers corresponding to
the respective zones. In this case, the moving average processing
may be performed on the data, obtained as the polishing table 112
rotates, in each zone.
[0153] FIG. 22 is a graph showing an example of a pre-polish
thickness and a post-polish thickness of a copper film formed on a
substrate having a diameter of 300 mm. In FIG. 22, the film
thickness was measured along a circumferential direction of the
substrate. As can be seen from FIG. 22, while the film thickness in
the middle zone (a radius r=116 mm) is approximately uniform,
considerable variations in the film thickness along the
circumferential direction are observed in the peripheral zone
(r=146 mm) of the substrate. This is because of the variations in
contact resistance of the cathode electrodes (negative electrodes)
arranged at equal intervals along the periphery of the substrate,
or the variations in sealing performance of the seal member for
retaining the plating solution. Possible causes of such variations
in the contact resistance and the sealing performance include
individual difference of parts, assembly error, and a secular
change of parts. In addition, when using a plating apparatus having
plural cells (plating baths) each for use in a plating process, the
variations in the film thickness along the circumferential
direction may differ depending on the cells. Moreover, the tendency
of the variations in the film thickness can be changed by
replacement of parts.
[0154] FIG. 23 is a view showing the sensor paths on the surface of
the substrate when the rotational speed of the polishing table 112
is set to 60 min.sup.-1 and the rotational speed of the top ring
114 is set to 31 min.sup.-1. In this example shown in FIG. 23, the
sensor path rotates gradually, as well as the example shown in FIG.
17. The top ring 114 rotates through 186 degrees while the
polishing table 112 makes one revolution (360-degree revolution).
Therefore, when ignoring the scanning direction, the sensor path is
returned to its original position after making half of one
revolution around the surface of the substrate in 30 seconds.
Therefore, if the moving average time is set to 5 seconds, the
sensor scans only a thick-film portion or a thin-film portion in
the periphery zone of the substrate W. This scanning operation may
result in overestimation or underestimation of the film
thickness.
[0155] FIG. 24 is a graph showing results of an operation example
in which the pressures in the four pressure chambers (air bags) P1,
P2, P3, and P4 of the top ring 114 are operated during polishing so
as to make the film thickness uniform in the zones C1, C2, C3, and
C4 distributed along the radial direction of the substrate W, under
the above-described rotational speed conditions. As can be seen
from FIG. 24, due to the influence of the variations in film
thickness in the periphery of the substrate W along the
circumferential direction, the pressure in outer pressure chamber
fluctuates in a cycle of 30 seconds more greatly than the pressure
in inner pressure chamber.
[0156] FIG. 25 is a view showing the sensor paths on the surface of
the substrate when the rotational speed of the polishing table 112
is adjusted to 60 min.sup.-1 and the rotational speed of the top
ring 114 is adjusted to 36 min.sup.-1 in order to avoid the above
problem. In this example, as can be seen from FIG. 25, the sensor
path makes substantially two revolutions in a counterclockwise
direction each time the polishing table 112 makes five revolutions.
During this period of time, the sensor 150 travels across the
surface of the substrate W in directions or orientations that are
distributed equally in the circumferential direction over the
circumference of the substrate W in it entirety.
[0157] FIG. 26 is a graph showing changes in the pressures in the
pressure chambers P1, P2, P3, and P4 of the top ring 114 when
polishing the substrate under the conditions as shown in FIG. 25.
In this example, the moving average time is set to 4 seconds. The
moving average is performed on data of five points obtained at
one-second intervals from a certain time back to a time by 4
seconds, i.e., data obtained while the polishing table 112 makes
five revolutions. As shown in FIG. 26, the pressure fluctuation in
a cycle of about 30 seconds as seen in FIG. 24 is not observed.
Therefore, it is supposed that an average film thickness with
respect to circumferential direction of the substrate is obtained
by the sensor 150.
[0158] A relationship between the rotational speed of the polishing
table 112 and the rotational speed of the top ring 114 for allowing
the sensor 150 to scan the surface of the substrate W at equal
angular intervals will now be described.
[0159] Where the sensor 150 sweeps across the surface of the
substrate W in directions or orientations distributed evenly in the
circumferential direction over the entire circumference of the
substrate W while the polishing table 112 makes a predetermined
number m (natural number) of revolutions, a relationship between a
rotational speed V of the polishing table 112 and a rotational
speed R of the top ring 114 is expressed by the following
equation.
R/V=n/m that is, mR/V=n (9)
[0160] In this equation (9), R represents the rotational speed of
the top ring;
[0161] V represents the rotational speed of the polishing
table;
[0162] m represents the predetermined number of revolutions (m is a
natural number) of the polishing table; and
[0163] n represents the predetermined number of revolutions the top
ring makes while the polishing table makes m revolution(s).
[0164] Where the sensor sweeps across the surface of the substrate
W evenly such that the sensor path rotates around the entire
circumference of the substrate w once while the polishing table
makes m revolutions, m and n are relatively prime.
[0165] The principle as a basis of the above equation (9) is as
follows. While the polishing table 112 makes m revolution(s), the
top ring 114 makes mR/V revolution(s). During this time, if the
sensor 150 travels across the surface of the substrate W in
directions or orientations distributed evenly in the
circumferential direction over the entire circumference thereof,
the top ring 114 is needed to make just n revolutions (see the
equation (9)), provided that such situation does not occur before
the polishing table 112 makes m revolutions (the top ring 114 makes
n revolutions). In other words, m and n are natural numbers that
are relatively prime.
[0166] From a different viewpoint of the equation (9), the
relationship between the rotational speed V of the polishing table
112 and the rotational speed R of the top ring 114 can also be
expressed by
|(V-R)/V|m=n' that is, |1-R/V|m=n' (10)
[0167] where n' is a natural number and represents the number of
revolutions the sensor path rotates on the surface of the substrate
until the sensor path returns to its initial direction.
[0168] In this case, when V>R,
mR/V=m-n', where n' is 1, 2, . . . , m-1.
When V<R.
mR/V=m+n', where n' is 1, 2, . . . .
[0169] Therefore, if m-n' is replaced with r when V>R or m+n' is
replaced with n when V<R, the equation (10) becomes equivalent
to the equation (9). Specifically, the number of revolutions n' of
the sensor path on the surface of the substrate is a difference
between the number of revolutions m of the polishing table 112 and
the number of revolutions n of the top ring 114.
[0170] In order to control the pressures in the pressure chambers
P1, P2, P3, and P4 in real time in response to a change in film
thickness during polishing, it is necessary to grasp a state of a
film surface at a point of time as close to a point of time when
determining the pressures as possible. For this reason, it is
preferable that the value m be relatively small. For example, in
order to grasp the surface state of the film within 16 seconds at
the latest from a pressure determination time, the value m should
be such that m/V.ltoreq.16 seconds. On the other hand, in order to
grasp an average surface state of the film without regard to the
variations in film thickness in the circumferential direction and
the difference in pattern density and structure, the value m is
needed to be relatively large. In a case where the variations in
film thickness in the circumferential direction are represented by
eight measurements corresponding to at least four scan lines, In is
not less than 4 (m.gtoreq.4). Therefore, in view of the real-time
control and the variations in film thickness, the number of
revolutions m is preferably such that
4.ltoreq.m.ltoreq.16.times.V.
[0171] FIG. 27 is a table showing examples of a ratio RN of the
rotational speeds of the top ring and the polishing table which
satisfies the equation (9). Actually, taking a polishing
performance of the polishing apparatus into consideration, an
appropriate ratio of the rotational speeds is selected from the
table, so that the rotational speed of the top ring 114 and the
rotational speed of the polishing table 112 are determined.
[0172] Due to some cause such as structures of the cell (i.e., the
plating bath) of the plating apparatus, a spatial periodicity on a
cycle of M may be observed in a change in film thickness at the
periphery of the substrate. In such a case, the relationship
between the rotational speed of the top ring 114 and the rotational
speed of the polishing table 112 is expressed by the following
equation.
R/V=n/(mM) n=1, 2, 3, (11)
[0173] If it is not until the polishing table 112 makes m
revolutions that the scan line scans evenly the film thicknesses
that vary along the circumferential direction of the substrate W, m
and n are natural numbers that are relatively prime.
[0174] When the rotational speed of the polishing table 112 is set
to an integral multiple of a setting unit (e.g., 1 min.sup.-1) of
the polishing apparatus based on the above equations (9), (10), and
(11), the rotational speed of the top ring 114 may not be an
integral multiple of the above-mentioned setting unit. In such a
case, an integer close to a value determined from the above
equations can be used for the rotational speed of the top ring 114.
When the rotational speed of the polishing table 112 and the
rotational speed of the top ring 114 are determined based on the
above equations, the same portion of the polishing pad 16 polishes
the same portion of the surface of the substrate W once, while the
polishing table 112 makes m revolutions. This can cause a locally
insufficient polishing of the substrate W due to the influence of
the grooves on the polishing pad 16. In such a case, it is
preferable to add or subtract a rotational speed which is the
setting unit (e.g., 1 min.sup.-1) of the polishing apparatus to or
from the rotational speed of the polishing table 112 or the top
ring 114.
[0175] For example, the rotational of the top ring 114 and the
rotational speed of the polishing table 112 can be established in a
range that is expressed by
nV/m-1.ltoreq.R.ltoreq.nV/m+1 (12)
or
mR/n-1.ltoreq.V.ltoreq.mR/n+1 (13)
[0176] where V is a rotational speed of the polishing table 112 and
is a natural number indicating a multiple of the setting unit that
is allowed by the polishing apparatus, and R is a rotational speed
of the top ring 114 and is a natural number indicating a multiple
of the setting unit that is allowed by the polishing apparatus.
[0177] Although the sensor 150 travels across the surface of the
substrate W in the directions or orientations that are distributed
evenly in the circumferential direction of the substrate W over its
entire circumference, it is not necessary from a practical
standpoint that the top ring 114 make just n revolutions while the
polishing table 112 makes m revolutions. If an allowable range of
revolution shift of the top ring 114 with respect to m revolutions
of the polishing table 112 is .+-.0.2 revolution, the rotational
speed of the polishing table 112 can be set within the following
range.
mR/(n+0.2).ltoreq.V.ltoreq.mR/(n-0.2) (14)
[0178] The above-described method can be applied not only to the
real-time control of the polishing process, but also to a process
of detecting a polishing end point and a process of simply
monitoring a film thickness. In the polishing control with the
purpose of providing a uniform film thickness, a film thickness in
the periphery of the substrate is regarded as important in most
cases. However, in the polishing end point detection and the simple
monitoring of the film thickness, it is not necessarily needed to
monitor the periphery of the substrate, and a film thickness only
in a central portion and/or its neighboring area may be monitored.
In the central portion and its surrounding area, a surface state of
substantially the same portion can be obtained even if the sensor
path rotates through 180 degrees. Therefore, in the polishing end
point detection and the simple monitoring of the film thickness, it
is possible to replace n with n/2 in the above equation (9). In
this case, the rotational speed ratio can be expressed by the
following equation.
R/V=n/(2m) (15)
[0179] In the above example, the moving average is used as a
smoothing method for reducing noise components in the monitoring
signal. However, any method can be used, as long as the method can
substantially smooth the noise components generated in the
monitoring signal in a cycle corresponding to the number of
revolutions m. For example, an infinite impulse response digital
filter may be used. Further, by appropriately setting a control
cycle (specifically, a cycle of changing the pressures in the
pressure chambers in response to the change in film thickness) so
as not to synchronize with the number of revolutions m, good
real-time control can be performed based on the monitoring signal
without using the smoothing process (e.g., moving average).
[0180] As described above, the present invention can be applied to
processing of the monitoring signal which indicates a polishing
state outputted from an In-situ sensor, such as an optical or eddy
current sensor, during planarization of a film formed on a surface
of a substrate, such as a semiconductor wafer, by chemical
mechanical polishing (CMP). The optical sensor is typically used in
polishing of a silicon oxide film that allows light to pass
therethrough. On the other hand, the eddy current sensor is used in
polishing of a conductive film such as metal. However, the optical
sensor can be used in polishing of a metal film with a thickness of
less than several tens nm, because such a thin metal film allows
light to pass therethrough.
[0181] The present invention can also be applied to a polishing
process in which a film is polished using the monitoring signal so
as to realize a uniform film thickness.
INDUSTRIAL APPLICABILITY
[0182] The present invention is applicable to processing end point
detection method and apparatus for detecting a timing of a
processing end point by calculating a characteristic value of a
surface of a workpiece (an object of polishing) such as a
substrate.
* * * * *